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Message-ID: <313da4c4e217a58e49e981f62d16bd15c97352bf.1794268615.git.alx@kernel.org>
Date: Tue, 10 Nov 2026 00:58:45 +0100
From: Alejandro Colomar <alx@...nel.org>
To: linux-man@...r.kernel.org
Cc: Alejandro Colomar <alx@...nel.org>, libc-alpha@...rceware.org,
Walter Harms <wharms@....de>, Rich Felker <dalias@...c.org>, ~hallyn/shadow@...ts.sr.ht,
musl@...ts.openwall.com
Subject: [PATCH v1] man/man3/crypt.3: These functions accept many algorithms,
not only DES
This page was written as if DES was the only portable algorithm, and
glibc was a weird one supporting other algorithms. These days (and
since a long time ago), DES has been long deprecated, and crypt(3)
supports many algorithms in all systems.
Signed-off-by: Alejandro Colomar <alx@...nel.org>
---
Hi!
The patch for documenting the detail about "*" will come later.
This was a cleanup that seemed necessary before doing that.
Let me know what you think about it. I'll reply with a copy of the
formatted page, so you don't need to apply the patch to review it.
Have a lovely night!
Alex
man/man3/crypt.3 | 84 ++++--------------------------------------------
1 file changed, 6 insertions(+), 78 deletions(-)
diff --git a/man/man3/crypt.3 b/man/man3/crypt.3
index 7c9a50a534b7..6c0511240898 100644
--- a/man/man3/crypt.3
+++ b/man/man3/crypt.3
@@ -47,56 +47,21 @@ .SH SYNOPSIS
.SH DESCRIPTION
.BR crypt ()
is the password hashing function.
-It is based on the Data Encryption
-Standard algorithm with variations intended (among other things) to
-discourage use of hardware implementations of a key search.
.P
.I key
is a user's typed password.
.P
.I salt
-is a two-character string chosen from the set
-.RB [ a\-zA\-Z0\-9./ ].
-This string is used to
-perturb the algorithm in one of 4096 different ways.
+is a string
+used for determining the hasing algorithm
+(possibly including parameters).
+It is also used to perturb the algorithm.
.P
-By taking the lowest 7 bits of each of the first eight characters of the
-.IR key ,
-a 56-bit key is obtained.
-This 56-bit key is used to encrypt repeatedly a
-constant string (usually a string consisting of all zeros).
The returned
-value points to the hashed password, a series of 13 printable ASCII
-characters (the first two characters represent the salt itself).
+value points to the hashed password.
The return value points to static data whose content is
overwritten by each call.
.P
-Warning: the key space consists of
-.if t 2\s-2\u56\s0\d
-.if n 2**56
-equal 7.2e16 possible values.
-Exhaustive searches of this key space are
-possible using massively parallel computers.
-Software, such as
-.BR crack (1),
-is available which will search the portion of this key space that is
-generally used by humans for passwords.
-Hence, password selection should,
-at minimum, avoid common words and names.
-The use of a
-.BR passwd (1)
-program that checks for crackable passwords during the selection process is
-recommended.
-.P
-The DES algorithm itself has a few quirks which make the use of the
-.BR crypt ()
-interface a very poor choice for anything other than password
-authentication.
-If you are planning on using the
-.BR crypt ()
-interface for a cryptography project, don't do it: get a good book on
-encryption and one of the widely available DES libraries.
-.P
.BR crypt_r ()
is a reentrant version of
.BR crypt ().
@@ -122,40 +87,6 @@ .SH ERRORS
.BR crypt ()
function was not implemented,
probably because of U.S.A.\& export restrictions.
-.\" The following level of detail is not necessary in this man page.
-.\" .P
-.\" When encrypting a plain text P using DES with the key K results in the
-.\" encrypted text C, then the complementary plain text P' being encrypted
-.\" using the complementary key K' will result in the complementary encrypted
-.\" text C'.
-.\" .P
-.\" Weak keys are keys which stay invariant under the DES key transformation.
-.\" The four known weak keys 0101010101010101, fefefefefefefefe,
-.\" 1f1f1f1f0e0e0e0e and e0e0e0e0f1f1f1f1 must be avoided.
-.\" .P
-.\" There are six known half weak key pairs, which keys lead to the same
-.\" encrypted data. Keys which are part of such key clusters should be
-.\" avoided.
-.\" Sorry, I could not find out what they are.
-.\""
-.\" .P
-.\" Heavily redundant data causes trouble with DES encryption, when used in the
-.\" .I codebook
-.\" mode that
-.\" .BR crypt ()
-.\" implements. The
-.\" .BR crypt ()
-.\" interface should be used only for its intended purpose of password
-.\" verification, and should not be used as part of a data encryption tool.
-.\" .P
-.\" The first and last three output bits of the fourth S-box can be
-.\" represented as function of their input bits. Empiric studies have
-.\" shown that S-boxes partially compute the same output for similar input.
-.\" It is suspected that this may contain a back door which could allow the
-.\" NSA to decrypt DES encrypted data.
-.\" .P
-.\" Making encrypted data computed using crypt() publicly available has
-.\" to be considered insecure for the given reasons.
.TP
.B EPERM
.I /proc/sys/crypto/fips_enabled
@@ -217,10 +148,7 @@ .SS Availability in glibc
.I libxcrypt
is an ABI-compatible drop-in replacement.
.SH NOTES
-.SS Features in glibc
-The glibc version of this function supports additional
-hashing algorithms.
-.P
+.SS salt
If
.I salt
is a character string starting with the characters
base-commit: b951aa8a5356e12f635650d0136abed715e0d607
--
2.55.0
Download attachment "signature.asc" of type "application/pgp-signature" (834 bytes)
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