From da7ba92a4e7ce07cde9348ffe7984f19a6e12821 Mon Sep 17 00:00:00 2001 From: Kurt Zeilenga Date: Wed, 28 May 2008 23:44:13 +0000 Subject: [PATCH] Some reworking. In particular, don't tout hashed passwords as being more secure than non-hashed passwords. --- doc/guide/admin/security.sdf | 43 ++++++++++++++++++++++++------------ 1 file changed, 29 insertions(+), 14 deletions(-) diff --git a/doc/guide/admin/security.sdf b/doc/guide/admin/security.sdf index b529c6853d..ccd9b0b010 100644 --- a/doc/guide/admin/security.sdf +++ b/doc/guide/admin/security.sdf @@ -173,26 +173,41 @@ mechanism. The {{SECT:Using SASL}} section discusses the use of SASL. H2: Password Storage LDAP passwords are normally stored in the {{userPassword}} attribute. -{{REF:RFC4519}} specifies that passwords are not stored in encrypted form, -but this can create an unwanted security exposure so {{slapd}} provides -several options for the administrator to choose from. +{{REF:RFC4519}} specifies that passwords are not stored in encrypted +(or hashed) form. This allows a wide range of password-based +authentication mechanisms, such as {{EX:DIGEST-MD5}} to be used. +This is also the most interoperable storage scheme. + +However, it may be desirable to store a hash of password instead. +{{slapd}}(8) supports a variety of storage schemes for the administrator +to choose from. + +Note: Values of password attributes, regardless of storage scheme +used, should be protected as if they were clear text. Hashed +passwords are subject to {{dictionary attacks}} and {{brute-force +attacks}}. The {{userPassword}} attribute is allowed to have more than one value, and it is possible for each value to be stored in a different form. During authentication, {{slapd}} will iterate through the values until it finds one that matches the offered password or until it -runs out of values to inspect. The storage scheme is stored as a prefix -on the value, so a Unix {{crypt}}-style password might look like this: +runs out of values to inspect. The storage scheme is stored as a prefix +on the value, so a hashed password using the Salted SHA1 ({{EX:SSHA}}) +scheme looks like: -> userPassword: {CRYPT}.7D8U/PCF00Hw +> userPassword: {SSHA}DkMTwBl+a/3DQTxCYEApdUtNXGgdUac3 -In general, it is safest to store passwords in a salted hashed format -like SSHA. This makes it very hard for an attacker to derive passwords -from stolen backups or by obtaining access to the on-disk {{slapd}} -database. +The advantage of hashed passwords is that is that an attacker which +discovers the hash does not have direct access to the actual password. +Unforunately, as dictionary and brute force attacks are generally +quite easy for attackers to successfully mount, this advantage is +marginal at best. (This is why all modern Unix systems use shadow +password files.) -The disadvantage of hashed storage is that it prevents the use of some -authentication mechanisms such as {{EX:DIGEST-MD5}}. +The disadvantages of hashed storage is they are non-standard, may +cause interoperability problems, and generally preclude the use +of stronger than Simple (or SASL/PLAIN) password-based authentication +mechanisms, such as {{EX:DIGEST-MD5}}. H3: SSHA password storage scheme @@ -219,8 +234,8 @@ transferred to or from an existing Unix password file without having to know the cleartext form. Both forms of {{crypt}} include salt so they have some resistance to dictionary attacks. -Note: Since this scheme uses the operation system's {{crypt(3)}} hash function, -it is therefore operation system specific. +Note: Since this scheme uses the operation system's {{crypt(3)}} +hash function, it is therefore operation system specific. H3: MD5 password storage scheme -- 2.39.5