Internet Draft P.Behera draft-behera-ldap-password-policy-01.txt V. Chu Intended Category: Proposed Standard Netscape Expires: September 2000 L. Poitou Sun Microsystems J. Sermersheim Novell March 2000 Password Policy for LDAP Directories Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 [1]. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. 1. Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Behera, et. al. Proposed Standard Page 1 Password Policy for LDAP Directories March 2000 2. Abstract Password policy is a set of rules that controls how passwords are used in LDAP directories. In order to improve the security of LDAP directories and make it difficult for password cracking programs to break into directories, it is desirable to enforce a set of rules on password usage. These rules are made to ensure that users change their passwords periodically, passwords meet construction requirements, the re-use of old password is restricted, and users are locked out after a certain number of failed attempts. 3. Overview LDAP-based directory services are currently accepted by many organizations as the access protocol for directories. The ability to ensure the secure read and update access to directory information throughout the network is essential to the successful deployment. Most LDAP implementations support many authentication schemes - the most basic and widely used is the simple authentication i.e., user DN and password. In this case, many LDAP servers have implemented some kind of policy related to the password used to authenticate. Among other things, this policy includes: - Whether and when passwords expire. - Whether failed bind attempts cause the account to be locked. - If and how users are able to change their passwords. In order to achieve greater security protection and ensure interoperability in a heterogeneous environment, LDAP needs to standardize on a common password policy model. This is critical to the successful deployment of LDAP directories. 4.1 Application of password policy The password policy defined in this document can be applied to any attribute holding usersÆ passwords which are used for authentication by the use of the bind operation. Typically, it is applied to the userPassword attribute in the case of the LDAP simple authentication method [RFC-2251] or the case of password based SASL [RFC-2222] authentication such as CRAM-MD5 [RFC- 2195] and HTTP-Digest [RFC-Digest]. The password policy also defines some constraints to be checked during add or modify operations on these attributes. In this document, the term "user" represents any application which is an LDAP client using the directory to retrieve or store information. Directory administrators are not forced to comply with any of password policy. In other words, the password for a directory administrator never expires, the account is never locked, etc. 5. Articles of password policy Behera, et. al. Proposed Standard Page 2 Password Policy for LDAP Directories March 2000 The following sections explain in general terms each aspect of the password policy defined in this document as well as the need for each. These policies are subdivided into the general groups of password usage and password modification. Implementation details are presented in sections 8 and 9. 5.1. Password Usage Policy This section describes policy enforced while users are using passwords to authenticate. The general focus of this policy is to minimize the threat of intruders once a password is in use. 5.1.1. Password Guessing limit In order to prevent intruders from guessing a user's password, a mechanism exists to track the number of failed authentication attempts, and take action when a limit is reached. This policy consists of five parts: - A configurable limit. - A counter to track the number of failed authentication attempts. - A timeframe in which the limit of consecutive failed authentication attempts must happen before action is taken. - The action to be taken when the limit is reached. The action will either be nothing, or the account will be locked. - An amount of time the account is locked (if it is to be locked). This can be indefinite. 5.2. Password Modification Policy This section describes policy enforced while users are modifying passwords. The general focus of this policy is to ensure that when users add or change their passwords, the security and effectiveness of their passwords is maximized. 5.2.1. Password Expiration, Expiration Warning, and Grace binds One of the key properties of a password is the fact that it is not well known. If a password is frequently changed, the chances of that user's account being broken into are minimized. Directory administrators may deploy a password policy which causes passwords to expire after a given amount of time û thus forcing users to change their passwords periodically. As a side effect, there needs to be a way in which users are made aware of this need to change their password before actually being Behera, et. al. Proposed Standard Page 3 Password Policy for LDAP Directories March 2000 locked out of their accounts. One or both of the following methods handle this: - The user is sent a warning sometime before his password is due to expire. If the user fails to heed this warning before the expiration time, his account will be locked. - The user may bind to the directory a preset number of times after her password has expired. If she fails to change her password during one of her 'grace' binds, her account will be locked. 5.2.2. Password History When the Password Expiration policy is used, an additional mechanism may be employed in order to prevent users from simply re-using a previous password (as this would effectively circumvent the expiration policy). In order to do this; a history of used passwords is kept. The directory administrator sets the number of passwords to be stored at any given time. Passwords are stored in this history whenever the password is changed. Users aren't allowed to specify any passwords that are in the history list while changing passwords. 5.2.3. Password Minimum Age Users may circumvent the Password History mechanism by quickly performing a series of password changes. If they change their password enough times, their 'favorite' password will be pushed out of the history list. This process may be made less attractive to users by employing a minimum age for passwords. If users are forced to wait 24 hours between password changes, they may be less likely to cycle through a history of 10 passwords. 5.2.4. Password Syntax and Minimum length In order to prevent users from creating or updating passwords that are easy to guess, a password syntax policy may be employed. This policy consists of two general mechanisms - ensuring that passwords conform to a defined syntax and ensuring that they are of a minimum length. Forcing a password to comply with a syntax may imply a variety of things including: - Disallowing trivial or well-known words make up the password. - Forcing a certain number of digits be used. - Disallowing anagrams of the user's name. Behera, et. al. Proposed Standard Page 4 Password Policy for LDAP Directories March 2000 The implementation of this policy meets with the following problems: - If the password to be added or updated is encrypted by the client before being sent, the server has no way of enforcing this policy. Therefore, the onus of enforcing this policy falls upon client implementations. - There are no specific definitions of what 'syntax checking' means. This can lead to unexpected behavior in a heterogeneous environment. 5.2.5. User Defined Passwords In some cases, it is desirable to disallow users from adding and updating their own passwords. This policy makes this functionality possible. This implies that certain other policy, such as password expiration is not enforced. 5.2.6. Password Change After Reset This policy forces the user to update her password after it has been set for the first time, or has been reset by the directory administrator. This is needed in scenarios where a directory administrator set or reset the password to a well-known value. 5.2.7 Safe modification As directories become more commonly used, it will not be unusual for clients to connect to a directory and leave the connection open for an extended period. This opens up the possibility for an intruder to make modifications to a user's password while that user's computer is connected but unattended. This policy forces the user to prove his identity by specifying the old password before modifying it. 6. Schema used for Password Policy The schema elements defined here fall into two general categories. A password policy object class is defined which contains a set of administrative password policy attributes, and a set of operational attributes are defined which hold general password policy state information for each user. 6.1. The pwdPolicy Object Class This object class holds password policy in effect for a set of users. See section 11 for a discussion of how entries of this object class are associated with users. Behera, et. al. Proposed Standard Page 5 Password Policy for LDAP Directories March 2000 ( pwdSchema.6.1 NAME 'pwdPolicy' AUXILIARY SUP top MUST ( pwdAttribute ) MAY ( pwdMinAge $ pwdMaxAge $ pwdInHistory $ pwdCheckSyntax $ pwdMinLength $ pwdDefaultStorageScheme $ pwdExpireWarning $ pwdGraceLoginLimit $ pwdLockout $ pwdLockoutDuration $ pwdMaxFailure $ pwdFailureCountInterval $ pwdMustChange $ pwdAllowUserChange $ pwdSafeModify ) ) 6.2. Attribute Types used in the pwdPolicy ObjectClass Following are the attribute types used by the pwdPolicy object class. 6.2.1 pwdAttribute This holds the name of the attribute to which the password policy is applied. For example, the password policy may be applied to the userPassword attribute. ( pwdSchema.4.1.1 NAME 'pwdAttribute' EQUALITY caseIgnoreMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.15 ) 6.2.2 pwdMinAge This attribute holds the number of seconds that must elapse between modifications to the password. If this attribute is not present, 0 seconds is assumed. ( pwdSchema.4.1.2 NAME 'pwdMinAge' EQUALITY integerMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE ) 6.2.3 pwdMaxAge This attribute holds the number of seconds after which a modified password will expire. If this attribute is not present, or if the value is 0 the password does not expire. ( pwdSchema.4.1.3 NAME 'pwdMaxAge' EQUALITY integerMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE ) Behera, et. al. Proposed Standard Page 6 Password Policy for LDAP Directories March 2000 6.2.4 pwdInHistory This attribute specifies the maximum number of used passwords stored in the pwdHistory attribute. If this attribute is not present, or if the value is 0, used passwords are not stored in the pwdHistory attribute and thus may be reused. ( pwdSchema.4.1.4 NAME 'pwdInHistory' EQUALITY integerMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE ) 6.2.5 pwdCheckSyntax This attribute indicates how the password syntax will be checked while being modified. If this attribute is not present, or if the value is '0', syntax checking will not be enforced. A value of '1' indicates that the syntax will be checked if the password is not hashed, otherwise it must be accepted. A value of '2' indicates that the syntax will be checked if the password is not hashed, otherwise the server must returned an error refusing the password. ( pwdSchema.4.1.5 NAME 'pwdCheckSyntax' EQUALITY integerMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE ) 6.2.6 pwdMinLength This attribute holds the minimum number of characters that must be used in a password, if syntax checking is enabled. If this attribute is not present, no minimum password length will be enforced. If the password is hashed, the server will, depending on the value of the pwdCheckSyntax attribute, either accept the password without checking it ('0' or '1') or refuse it ('2'). ( pwdSchema.4.1.6 NAME 'pwdMinLength' EQUALITY integerMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE ) 6.2.7 pwdDefaultStorageScheme This attribute specifies the type of hash algorithm used to store directory server passwords. This is used when a password modification is made and the supplied password has not been Behera, et. al. Proposed Standard Page 7 Password Policy for LDAP Directories March 2000 encrypted. If this attribute is not present, or if the value is "CLEARTEXT", the password will not be changed before it is stored. The description of password storage scheme can be found in [RFC- 2307]. One additional storage scheme not mentioned there is "CLEARTEXT". ( pwdSchema.4.1.7 NAME 'pwdDefaultStorageScheme' EQUALITY caseIgnoreMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.15 SINGLE-VALUE ) 6.2.8 pwdExpireWarning This attribute specifies the maximum number of seconds before a password is due to expire that expiration warning messages will be returned to an authenticating user. If this attribute is not present, or if the value is 0 no warnings will be sent. ( pwdSchema.4.1.8 NAME 'pwdExpireWarning' EQUALITY integerMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE ) 6.2.9 pwdGraceLoginLimit This attribute specifies the number of times an expired password can be used to access an account. If this attribute is not present or if the value is 0, the account cannot be accessed once the password has expired. ( pwdSchema.4.1.9 NAME 'pwdGraceLoginLimit' EQUALITY integerMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE ) 6.2.10 pwdLockout This attribute indicates, when its value is "TRUE", that users will be locked out of the directory after a specified number of consecutive failed bind attempts. The maximum number of consecutive failed bind attempts is specified in pwdMaxFailure. If this attribute is not present, or if the value is "FALSE", the account will not be locked when the number of failed bind attempts has been reached. ( pwdSchema.4.1.10 NAME 'pwdLockout' EQUALITY booleanMatch Behera, et. al. Proposed Standard Page 8 Password Policy for LDAP Directories March 2000 SYNTAX 1.3.6.1.4.1.1466.115.121.1.7 SINGLE-VALUE ) 6.2.11 pwdLockoutDuration This attribute holds the number of seconds that an account will remain locked due to too many failed bind attempts. If this attribute is not present, or if the value is 0 the account will be locked until reset by an administrator. ( pwdSchema.4.1.11 NAME 'pwdLockoutDuration' EQUALITY integerMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE ) 6.2.12 pwdMaxFailure This attribute specifies the number of consecutive failed bind attempts after which a users account will be locked. If this attribute is not present, or if the value is 0, the account will not be locked due to failed bind attempts and the value of pwdLockout will be ignored. ( pwdSchema.4.1.12 NAME 'pwdMaxFailure' EQUALITY integerMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE ) 6.2.13 pwdFailureCountInterval This attribute holds the number of seconds after which the password failures are purged from the failure counter. If this attribute is not present, or if its value is 0, the failure counter will never be purged. ( pwdSchema.4.1.13 NAME 'pwdFailureCountInterval' EQUALITY integerMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE ) 6.2.14 pwdMustChange This attribute specifies with a value of "TRUE" that users must change their passwords when they first bind to the directory after a password is set or reset by the administrator. If this attribute is not present, or if the value is "FALSE", users are not required to change their password upon binding after the administrator sets or resets the password. Behera, et. al. Proposed Standard Page 9 Password Policy for LDAP Directories March 2000 ( pwdSchema.4.1.14 NAME 'pwdMustChange' EQUALITY booleanMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.7 SINGLE-VALUE ) 6.2.15 pwdAllowUserChange This attribute indicates whether users can change their own passwords. If this attribute is not present, a value of "TRUE" is assumed. ( pwdSchema.4.1.15 NAME 'pwdAllowUserChange' EQUALITY booleanMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.7 SINGLE-VALUE ) 6.2.16 pwdSafeModify This attribute specifies whether or not the existing password must be sent when changing a password. If this attribute is not present, a "FALSE" value is assumed. ( pwdSchema.4.1.16 NAME 'pwdSafeModify' EQUALITY booleanMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.7 SINGLE-VALUE ) 6.3. Attribute Types for Password Policy State Information Password policy state information must be maintained for each user. The information is located in each user entry as a set of operational attributes. These operational attributes are: pwdChangedTime, pwdAccountLockedTime, pwdExpirationWarned, pwdFailureTime, pwdHistory, pwdGraceLeft, pwdReset. Since the password policy could apply to several attributes used to store passwords, each of the above operational attributes must have an option to tell which attribute is applies to. The password policy option is defined as the following: pwd- For example, if the pwdPolicy object has for pwdAttribute ôuserPasswordö then the pwdChangedTime operational attribute, in a user entry, will be like this: pwdChangedTime;pwd-userPassword: 20000103121520Z 6.3.1 pwdChangedTime Behera, et. al. Proposed Standard Page 10 Password Policy for LDAP Directories March 2000 This attribute specifies the time the entry's password was last changed. This is used by the password expiration policy. If this attribute does not exist, the password will never expire. ( pwdSchema.4.2.1 NAME 'pwdChangedTime' DESC 'The time the password was last changed' SYNTAX 1.3.6.1.4.1.1466.115.121.1.24 EQUALITY generalizedTimeMatch ORDERING generalizedTimeOrderingMatch SINGLE-VALUE USAGE directoryOperation) 6.3.2 pwdAccountLockedTime This attribute holds the time that the userÆs account was locked. A 0 value means that the account has been locked permanently, and that only an administrator can unlock the account. ( pwdSchema.2.2 NAME 'pwdAccountLockedTime' DESC 'The time an user account was locked' SYNTAX 1.3.6.1.4.1.1466.115.121.1.24 EQUALITY generalizedTimeMatch ORDERING generalizedTimeOrderingMatch SINGLE-VALUE USAGE directoryOperation) 6.3.3 pwdExpirationWarned This attribute contains the time when the password expiration warning was first sent to the client. The password must expire in the pwdExpireWarning time. ( pwdSchema.2.3 NAME 'pwdExpirationWarned' DESC 'The time the user was first warned about the coming expiration of the password' SYNTAX 1.3.6.1.4.1.1466.115.121.1.24 EQUALITY generalizedTimeMatch ORDERING generalizedTimeOrderingMatch SINGLE-VALUE USAGE directoryOperation ) 6.3.4 pwdFailureTime This attribute holds the time stamps of the consecutive authentication failures. ( pwdSchema.2.4 NAME 'pwdFailureTime' DESC 'The timestamps of the last consecutive authentication failures' Behera, et. al. Proposed Standard Page 11 Password Policy for LDAP Directories March 2000 SYNTAX 1.3.6.1.4.1.1466.115.121.1.24 EQUALITY generalizedTimeMatch ORDERING generalizedTimeOrderingMatch USAGE directoryOperation ) 6.3.5 pwdHistory This attribute holds a history of previously used passwords. Values of this attribute are transmitted in string format as given by the following BNF: pwdHistory = time "{" hashMethod "}" data time = hashMethod = data = criticality: FALSE controlValue:an OCTET STRING, whose value is the BER encoding of the following type: PasswordPolicyControlValue ::= SEQUENCE { warning [0] CHOICE OPTIONAL { timeBeforeExpiration [0] INTEGER (0 .. maxInt), graceLoginsRemaining [1] INTEGER (0 .. maxInt) } error [1] ENUMERATED OPTIONAL { passwordExpired (0), accountLocked (1), changeAfterReset (2), passwordModNotAllowed (3), mustSupplyOldPassword (4), invalidPasswordSyntax (5), passwordTooShort (6), passwordTooYoung (7), passwordInHistory (8) } The timeBeforeExpiration warning specifies the number of seconds before a password will expire. The graceLoginsRemaining warning specifies the remaining number of time a user will be allowed to authenticate with an expired password. The passwordExpired error signifies that the password has expired and must be reset. The changeAfterReset error signifies that the password must be changed before the user will be allowed to perform any operation other than bind and modify. The passwordModNotAllowed is set when a user is restricted from changing her password. The invalidPasswordSyntax error is set when a password doesn't pass syntax checking. The passwordTooYoung is set if the age of the password to be modified is not yet old enough. Typically, only either a warning or an error will be encoded though there may be exceptions. For example, if the user is required to change a password after the administrator set it, and the password Behera, et. al. Proposed Standard Page 13 Password Policy for LDAP Directories March 2000 will expire in a short amount of time, the control may include the timeBeforeExpiration warning and the changeAfterReset error. 8. Server Implementation by LDAP operation The following sections contain detailed instructions that refer to attributes of the pwdPolicy object class. When doing so, the attribute of the pwdPolicy object that governs the entry being discussed is implied. The server should enforce that the password attribute subject to a password policy as defined in this document, contains one and only one password value. 8.1 Bind Operation When processing a bind request, the server performs the following steps: 1. Checks for a locked account: If the value of the pwdAccountLockedTime attribute is 0, or if the current time is less than the value of the pwdAccountLockedTime attribute added to the value of the pwdLockoutDuration, the account is locked. If the account is locked, the server sends a bindResponse to the client with the resultCode: unwillingToPerform (53), and includes the passwordPolicyControl in the controls field of the bindResponse message with the error: accountLocked (1). 2. If the account is not locked, the server proceeds with the bind operation and checks the result: If the bind operation succeeds with authentication, The server does the following: A. Deletes the pwdFailureTime attribute. B. Checks whether the password must be changed now. If the pwdMustChange attribute is set to TRUE, and if the pwdReset attribute is set to TRUE, the server sends a bindResponse to the client with the resultCode: success (0), and includes the passwordPolicyControl in the controls field of the bindResponse message with the warning: changeAfterReset specified. The server then disallows all operations issued by this user except modify password, bind, unbind, and abandon. C. Checks for password expiration If the value of the pwdExpireWarning attribute is 0, the server subtracts the current time from the time stored in pwdChangedTime to arrive at the password's age. If the age is Behera, et. al. Proposed Standard Page 14 Password Policy for LDAP Directories March 2000 greater than the value in the pwdMaxAge attribute, the password has expired. If the value of the pwdExpireWarning attribute is non-0, and the pwdExpirationWarned attribute is present and has a positive value, the server subtracts the current time from the time stored in the pwdExpirationWarned to arrive at the first warning age. If the age is greater than the value in the pwdExpireWarning attribute, the password has expired. In the case of an expired password, the server checks for remaining grace logins - The server checks the pwdGraceLeft attribute. A non-0 value means there are that many remaining grace logins. - If there are remaining grace logins, the server decrements the value in pwdGraceLeft by 1 and sends a bindResponse with the resultCode: success (0), and includes the passwordPolicyControl in the controls field of the bindResponse message with the warning: graceLoginsRemaining choice set to the number of grace logins left. - If there are no remaining grace logins, the server sends a bindResponse with the resultCode: invalidCredentials (49), and includes the passwordPolicyControl in the controls field of the bindResponse message with the error: passwordExpired (0) set. D. Calculates whether the time before expiration warning should be sent. If the pwdExpirationWarned attribute is present and has a positive value, the warning is sent with a timeBeforeExpiration set to the value of the pwdExpirationWarned attribute plus the value of the pwdExpireWarning attribute minus the current time. Otherwise, the server subtracts the current time from the time stored in pwdChangedTime to arrive at the password's age. If the age is greater than the value of the pwdMaxAge attribute minus the value of the pwdExpireWarning attribute, the server sets the current time as the value of the pwdExpirationWarned attribute, and the warning is sent with a timeBeforeExpiration set to the value of pwdMaxAge minus the passwordÆs age. The server sends a bindResponse with the resultCode: success (0), and includes the passwordPolicyControl in the controls field of the bindResponse message with the warning: timeBeforeExiration set to the value as described above. If the bind operation fails authentication due to invalid credentials and the pwdLockout attribute is TRUE, the server does the following: Behera, et. al. Proposed Standard Page 15 Password Policy for LDAP Directories March 2000 A. Adds the current time as a value of the pwdFailureTime attribute. B. Counts the number of values in the pwdFailureTime attribute that are younger than pwdFailureCountInterval. If the number of these failures is greater or equal to the pwdMaxFailure attribute, the server locks the account by setting the value of the pwdAccountLockedTime attribute to the current time. After locking the account, the server sends a bindResponse to the client with the resultCode: unwillingToPerform (53), and includes the passwordPolicyControl in the controls field of the bindResponse message with the error: accountLocked (1). C. Failures times that are old by more than pwdFailureCountInterval, are purged from the pwdFailureTime attribute. 8.2. Modify Operation Because the password is stored in an attribute, the modify operation may be used to create or update a password. Other specifications MAY define alternate mechanisms used to modify the password. The following instructions are to be followed when processing any request which includes changes to the password attribute. While processing a password modification, the server performs the following steps: 1. Checks the pwdSafeModify attribute. If set, the server ensures that the modify operation contains a delete action before the add or replace action, and that the delete action specifies the existing password. If the delete action is not specified, the server aborts the modification and then sends a modifyResponse to the client with the resultCode: unwillingToPerform (53), and includes the passwordPolicyControl in the controls field of the modifyResponse message with the error: mustSupplyOldPassword (4). 2. Checks the value of the pwdMustChange attribute. If TRUE, the server checks the pwdReset attribute in the userÆs entry, to see if the password has been reset by a Directory Administrator. If so, it ensures that the modify operation contains no modifications other than the modification of the password attribute. If other modifications exist, the server sends a modifyResponse to the client with the resultCode: unwillingToPerform (53), and includes the passwordPolicyControl in the controls field of the modifyResponse message with the error: changeAfterReset (2). 3. Checks to see whether the bound identity has sufficient rights to modify the password. If the bound identity is a user changing her own password, this may be done by either the use of an access control mechanism, or by checking the pwdAllowUserChange Behera, et. al. Proposed Standard Page 16 Password Policy for LDAP Directories March 2000 attribute. Otherwise an access control mechanism must be used. The determination of this is implementation specific. If the user is not allowed to change her password, the server sends a modifyResponse to the client with the resultCode: unwillingToPerform (53), and includes the passwordPolicyControl in the controls field of the modifyResponse message with the error: passwordModNotAllowed (3). 4. Checks the value of the pwdMinAge attribute. If it is set to a non-0 value, the server subtracts the current time from the value of the pwdChangedTime attribute to arrive at the password's age. If the password's age is less than the value of the pwdMinAge attribute, the password is too young to modify. In this case, the server sends a modifyResponse to the client with the resultCode: constraintViolation (19), and includes the passwordPolicyControl in the controls field of the modifyResponse message with the error: passwordTooYoung (7). 5. Checks the value of the pwdCheckSyntax attribute. If the value is non-0, The server: A. ensures that the password meets the syntax restrictions enforced by the server. This enforcement is implementation specific. If the password fails this check or the password is hashed and the value of the pwdCheckSyntax attribute is 2, the server sends a modifyResponse to the client with the resultCode: constraintViolation (19), and includes the passwordPolicyControl in the controls field of the modifyResponse message with the error: invalidPasswordSyntax (5). B. Checks the value of the pwdMinLength attribute. If the value is non-0, ensures that the new password is of at least the minimum length. If not or if the password is hashed and the value of the pwdCheckSyntax attribute is 2, the server sends a modifyResponse to the client with the resultCode: constraintViolation (19), and includes the passwordPolicyControl in the controls field of the modifyResponse message with the error: passwordTooShort (6). 6. Checks the value of the pwdStorageScheme attribute. If the pwdStorageScheme is other than "CLEARTEXT", the server hashes the password with the appropriate mechanism prior to storing. 7. Checks the value of the pwdInHistory attribute. If the value is non-0, the server checks whether this password exists in the entry's pwdHistory attribute or in the current password attribute. If the password does exist in the pwdHistory attribute or in the current password attribute, the server sends a modifyResponse to the client with the resultCode: constraintViolation (19), and includes the passwordPolicyControl Behera, et. al. Proposed Standard Page 17 Password Policy for LDAP Directories March 2000 in the controls field of the modifyResponse message with the error: passwordInHistory (8). If these steps have completed without causing an error condition, the server follows these steps in order to update the necessary password policy state attributes: 8. Checks the value of the pwdMaxAge attribute. If the value is non- 0, or if the value of the pwdMinAge attribute is non-0, the server updates the pwdChangedTime attribute on the entry to the current time. 9. If the value of the pwdInHistory attribute is non-0, the server adds the previous password to the pwdHistory attribute. If the number of attributes held in the pwdHistory attribute exceeds the value of pwdInHistory, the server removes the oldest excess passwords. 10.Checks the value of the pwdGraceLoginLimit attribute. If the value is non-0, resets the pwdGraceLeft attribute to the value held by the pwdGraceLoginLimit attribute in the pwdPolicy object in effect for this entry. 11.Removes the pwdFailureTime, pwdReset and pwdExpirationWarned attributes from the user's entry if they exist. The server then applies the modify operation. 8.3 Add Operation The password MAY be set during an Add operation. If it is, the server performs the following steps while processing the add operation: Note that these are essentially duplicates of steps 3, 5 and 6 from section 8.2. 1. Checks to see whether the bound identity has sufficient rights to modify the password. This may be done by the use of an access control mechanism. If the user is not allowed to add this password, the server sends an addResponse to the client with the resultCode: unwillingToPerform (53), and includes the passwordPolicyControl in the controls field of the addResponse message with the error: passwordModNotAllowed (3). 2. Checks the value of the pwdCheckSyntax attribute. If the value is non-0: A. ensures that the password meets the syntax restrictions enforced by the server. This enforcement is implementation specific. If the password fails this check or the password is hashed and the value of the pwdCheckSyntax attribute is 2, the server sends a modifyResponse to the client with the resultCode: constraintViolation (19), and includes the Behera, et. al. Proposed Standard Page 18 Password Policy for LDAP Directories March 2000 passwordPolicyControl in the controls field of the modifyResponse message with the error: invalidPasswordSyntax (5). B. Checks the value of the pwdMinLength attribute. If the value is non-0, ensures that the new password is of at least the minimum length. If not or if the password is hashed and the value of the pwdCheckSyntax attribute is 2, the server sends a modifyResponse to the client with the resultCode: constraintViolation (19), and includes the passwordPolicyControl in the controls field of the modifyResponse message with the error: passwordTooShort (6). 3. Checks the value of the pwdStorageScheme attribute. If the pwdStorageScheme is other than "CLEARTEXT", the server hashes the password with the appropriate mechanism prior to storing. If these steps have completed without causing an error condition, the server follows these steps in order to update the necessary password policy state attributes: Note that these are essentially duplicates of steps 8 and 10, from section 8.2. 4. Checks the value of the pwdMaxAge attribute. If the value is non- 0, or if the value of the pwdMinAge attribute is non-0, the server updates the pwdChangedTime attribute on the entry to the current time. 5. Checks the value of the pwdGraceLoginLimit attribute. If the value is non-0, sets the pwdGraceLeft attribute to the value held by the pwdGraceLoginLimit attribute in the pwdPolicy object in effect for this entry. 8.4 Compare Operation The compare operation MAY be used to compare a password. This might be performed when a client wishes to verify that user's supplied password is correct. An example of this is an LDAP HTTP authentication redirector. It may be desirable to use this rather than performing a bind operation in order to reduce possible overhead involved in performing a bind. ACLs may be used to restrict this comparison from being made. If a server supports this behavior, it MUST comply with the following. Otherwise the password policy described in this document may be circumvented. While comparing password attributes, the server performs the following steps: 1. Checks for a locked account: If the value of the pwdAccountLockedTime attribute is 0, or if the current time is less than the value of the pwdAccountLockedTime attribute added to the value of the Behera, et. al. Proposed Standard Page 19 Password Policy for LDAP Directories March 2000 pwdLockoutDuration, the account is locked. If the account is locked, the server sends a compareResponse to the client with the resultCode: unwillingToPerform (53), and includes the passwordPolicyControl in the controls field of the compareResponse message with the error: accountLocked (1). 2. If ACLs permit, the server proceeds with compare operation and checks the result. If the result of the compare operation is compareTrue, the server does the following: A. Deletes the pwdFailureTime attribute. B. Checks for password expiration If the value of the pwdExpireWarning attribute is 0, the server subtracts the current time from the time stored in pwdChangedTime to arrive at the password's age. If the age is greater than the value in the pwdMaxAge attribute, the password has expired. If the value of the pwdExpireWarning attribute is non-0, and the pwdExpirationWarned attribute is present and has a positive value, the server subtracts the current time from the time stored in the pwdExpirationWarned to arrive at the first warning age. If the age is greater than the value in the pwdExpireWarning attribute, the password has expired. In the case of an expired password, the server checks for remaining grace logins - The server checks the pwdGraceLeft attribute. A non-0 value means there are that many remaining grace logins. - If there are remaining grace logins, the server decrements the value in pwdGraceLeft by 1 and sends a bindResponse with the resultCode: success (0), and includes the passwordPolicyControl in the controls field of the bindResponse message with the warning: graceLoginsRemaining choice set to the number of grace logins left. - If there are no remaining grace logins, the server sends a bindResponse with the resultCode: invalidCredentials (49), and includes the passwordPolicyControl in the controls field of the bindResponse message with the error: passwordExpired (0) set. C. Calculates whether the time before expiration warning should be sent. If the pwdExpirationWarned attribute is present and has a positive value, the warning is sent with a timeBeforeExpiration set to the value of the pwdExpirationWarned attribute plus the value of the pwdExpireWarning attribute minus the current time. Behera, et. al. Proposed Standard Page 20 Password Policy for LDAP Directories March 2000 Otherwise, the server subtracts the current time from the time stored in pwdChangedTime to arrive at the password's age. If the age is greater than the value of the pwdMaxAge attribute minus the value of the pwdExpireWarning attribute, the server sets the current time as the value of the pwdExpirationWarned attribute, and the warning is sent with a timeBeforeExpiration set to the value of pwdMaxAge minus the passwordÆs age. The server sends a bindResponse with the resultCode: success (0), and includes the passwordPolicyControl in the controls field of the bindResponse message with the warning: timeBeforeExiration set to the value as described above. If the result of the compare operation is compareFalse, the server does the following: A. Adds the current time as a value of the pwdFailureTime attribute. B. Counts the number of values in the pwdFailureTime attribute that are younger than pwdFailureCountInterval. If the number of these failures is greater or equal to the pwdMaxFailure attribute, the server locks the account by setting the value of the pwdAccountLockedTime attribute to the current time. After locking the account, the server sends a bindResponse to the client with the resultCode: unwillingToPerform (53), and includes the passwordPolicyControl in the controls field of the bindResponse message with the error: accountLocked (1). C. Failures times that are old by more than pwdFailureCountInterval, are purged from the pwdFailureTime attribute. 9. Client Implementation by LDAP operation These sections illustrate possible scenarios for each LDAP operation and define the types of responses that identify those scenarios. 9.1. Bind Operation For every bind response received, the client checks the resultCode of the bindResponse and checks for a passwordPolicyControl to determine if any of the following conditions are true and may prompt the user accordingly. 1. The user is binding for the first time after the directory administrator set the password. In this scenario, the client may prompt the user to change his password immediately. resultCode: success (0) passwordPolicyControl: error: changeAfterReset (2) Behera, et. al. Proposed Standard Page 21 Password Policy for LDAP Directories March 2000 2. The user's password will expire in n number of seconds. resultCode: success (0) passwordPolicyControl: warning: timeBeforeExpiration [0] INTEGER 3. The password failure limit has been reached and the account is locked. The user needs to retry later or contact the directory administrator to reset the password. resultCode: unwillingToPerform (53) passwordPolicyControl: error: accountLocked (1) 4. The password has expired but there are remaining grace logins. The user needs to change it. resultCode: success (0) passwordPolicyControl: warning: graceLoginsRemaining [1] INTEGER 5. The password has expired and there are no more grace logins. The user needs to contact the directory administrator to reset the password. resultCode: invalidCredentials (49) passwordPolicyControl: error: passwordExpired (0) 9.2 Modify Operations 9.2.1 Modify Request If the application or client encrypts the password prior to sending it in a password modification operation (whether done through modifyRequest or another password modification mechanism), it SHOULD check the values of the pwdMinLength, pwdCheckSyntax, and pwdDefaultStorageScheme attributes and enforce these policies. 9.2.2 Modify Response If the modifyRequest operation was used to change the password, or if another mechanism is used--such as an extendedRequest--the modifyResponse or other appropriate response may contain information pertinent to password policy. The client checks the resultCode of the response and checks for a passwordPolicyControl to determine if any of the following conditions are true and optionally notify the user of the condition. 1. The user attempted to change her password without specifying the old password but the password policy requires this. resultCode: unwillingToPerform (53) passwordPolicyControl: error: mustSupplyOldPassword (4) 2. The user must change her password before submitting any other LDAP requests. Behera, et. al. Proposed Standard Page 22 Password Policy for LDAP Directories March 2000 resultCode: unwillingToPerform (53) passwordPolicyControl: error: changeAfterReset (2) 3. The user doesn't have sufficient rights to change his password. resultCode: unwillingToPerform (53) passwordPolicyControl: error: passwordModNotAllowed (3) 4. It is too soon after the last password modification to change the password. resultCode: constraintViolation (19) passwordPolicyControl: error: passwordTooYoung (7) 5. The length of the password is too short. resultCode: constraintViolation (19) passwordPolicyControl: error: passwordTooShort (6) 6. The password failed syntax checking. resultCode: constraintViolation (19) passwordPolicyControl: error: invalidPasswordSyntax (5) 7. The password has already been used; the user must choose a different one. resultCode: constraintViolation (19) passwordPolicyControl: error: passwordInHistory (8) 9.3 Add Operation If a password is specified in an addRequest, the client checks the resultCode of the addResponse and checks for a passwordPolicyControl to determine if any of the following conditions are true and may prompt the user accordingly. 1. The user doesn't have sufficient rights to add this password. resultCode: unwillingToPerform (53) passwordPolicyControl: error: passwordModNotAllowed (3) 2. The length of the password is too short. resultCode: constraintViolation (19) passwordPolicyControl: error: passwordTooShort (6) 3. The password failed syntax checking. resultCode: constraintViolation (19) passwordPolicyControl: error: invalidPasswordSyntax (5) Behera, et. al. Proposed Standard Page 23 Password Policy for LDAP Directories March 2000 9.4 Other Operations For operations other than bind, unbind, abandon, or search, the client checks the following result code and control to determine if the user needs to change the password immediately. 1. The user needs to change password. The user should be prompted to change the password immediately. resultCode: unwillingToPerform (53) passwordPolicyControl: error: changeAfterReset (2) 10. Association between Users and Password Policy A password policy should be defined as a subentry [SubEntry] of the portion of the DIT to which it applies. When the server need to find the password policy that applies to a specific user and password attribute, it will try to locate the nearest subentry of objectclass pwdPolicy whose pwdAttribute matches the desired password attribute. If several policies are defined in the same portion of the DIT, it is up to the administrators to ensure that thereÆs no conflict, otherwise results could be undetermined. 11. Password Policy and Replication The pwdPolicy object defines the password policy for a portion of the DIT and must be replicated on all the replicas of this subtree, as any subentry would be. The elements of the password policy that are related to the users are stored in the entry themselves as operational attributes. As these attributes are subject to modifications even on a read-only replica, replicating them must be carefully considered. The pwdChangedTime attribute must be replicated on all replicas, to allow expiration of the password. The pwdReset attribute must be replicated on all replicas, to deny access to operations other than bind and modify password. The pwdHistory attribute must be replicated to writable replicas. It doesnÆt have to be replicated to a read-only replica, since the password will never be directly modified on this server. The pwdAccountLockedTime, pwdExpirationWarned, pwdFailureTime and pwdGraceLeft attributes must be replicated to writable replicas, making the password policy global for all servers. When the user, entry is replicated to a read-only replica, these attributes should not be replicated. This means that the number of failures, of grace logins and the locking will take place on each replicated server. For example, the effective number of failed Behera, et. al. Proposed Standard Page 24 Password Policy for LDAP Directories March 2000 attempts on a user password will be N x M (where N is the number of servers and M the value of pwdMaxFailure attribute). Replicating these attributes to a read-only replica may reduce the number of tries globally but may also introduce some inconstancies in the way the password policy is applied. 12. Security Considerations This document defines a set of rules to implement in an LDAP server, in order to improve the security of LDAP directories and make it difficult for password cracking programs to break into directories. Because the state information in the userÆs entry is on a per attribute basis and not per password attribute value, the server should enforce that the password attribute subject to a password policy as defined in this document, contains one and only one password value. 13. Bibliography [RFC-2251] Wahl, M., Howes, T., Kille, S., "Lightweight Directory Access Protocol (v3)", RFC 2251, August 1997. [RFC-2252] Wahl, M., Coulbeck, A., Howes, T., Kille, S., "Lightweight Directory Access Protocol (v3): Attribute Syntax Definitions", RFC 2252, December 1997. [RFC-2307] L. Howard, "An Approach for Using LDAP as a Network Information Service", RFC 2307, March 1998. [RFC-2119] S. Bradner, "Key Words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. [RFC-2222] J. Myers, "Simple Authentication and Security Layer (SASL)", RFC 2222, October 1997. [RFC-2195] J. Klensin, R. Catoe, P. Krumviede, "IMAP/POP AUTHorize Extension for Simple Challenge/Response", RFC 2195, September 1997. [RFC-Digest] Paul J. Leach, Chris Newman, "Using Digest Authentication as a SASL Mechanism", draft-leach-digest-sasl-05.txt, October 1999. [SubEntry] Ed Reed, "LDAP Subentry schema", draft-ietf-ldup- subentry-01.txt, August 1999. 14. Authors' Addresses Prasanta Behera Netscape Communications Corp. Behera, et. al. Proposed Standard Page 25 Password Policy for LDAP Directories March 2000 501 E. Middlefield Rd. Mountain View, CA 94043 USA +1 650 937-4948 prasanta@netscape.com Valerie Chu Netscape Communications Corp. 501 E. Middlefield Rd. Mountain View, CA 94043 USA +1 650 937-3443 vchu@netscape.com Ludovic Poitou Sun Microsystems Inc. 32 Chemin du vieux chŠne 38240 Meylan France +33 476 414 212 ludovic.poitou@france.sun.com Jim Sermersheim Novell, Inc. 122 East 1700 South Provo, Utah 84606, USA +1 801 861-3088 jimse@novell.com Behera, et. al. Proposed Standard Page 26