Re: RFC comments in lib / gc-pbkdf2-sha1.c

[Simon Josefsson]

Vladimir 'phcoder' Serbinenko <address@hidden> writes:

> Hello, all. When importing some gnulib code to GRUB2 I stumbled across 
> lib / gc-pbkdf2-sha1.c having comments taken from RFC2898. As far as I
> know RFC licence prohibits modifications. This seems to be GPL-incompatible.
> So is there are any licencing problem with this file?

Thanks for the report, I rewrote the comments to not use copyrighted
words from elsewhere.

/Simon

>From 24a6641b053b7fc8bf13b4149722e85d77db9920 Mon Sep 17 00:00:00 2001
From: Simon Josefsson <address@hidden>
Date: Sun, 15 Nov 2009 13:52:55 +0100
Subject: [PATCH] lib/gc-pbkdf2-sha1.c: Remove comments from RFC 2898.

---
 ChangeLog            |    5 +++
 lib/gc-pbkdf2-sha1.c |   99 ++++----------------------------------------------
 2 files changed, 13 insertions(+), 91 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index a241c5b..9fe5174 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2009-11-15  Simon Josefsson  <address@hidden>
+
+       * lib/gc-pbkdf2-sha1.c: Remove comments from RFC 2898.  Reported
+       by Vladimir 'phcoder' Serbinenko <address@hidden>.
+
 2009-11-14  Eric Blake  <address@hidden>
 
        fnmatch: avoid compiler warning
diff --git a/lib/gc-pbkdf2-sha1.c b/lib/gc-pbkdf2-sha1.c
index 3c864c6..0f5211b 100644
--- a/lib/gc-pbkdf2-sha1.c
+++ b/lib/gc-pbkdf2-sha1.c
@@ -1,5 +1,5 @@
 /* gc-pbkdf2-sha1.c --- Password-Based Key Derivation Function a'la PKCS#5
-   Copyright (C) 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
+   Copyright (C) 2002, 2003, 2004, 2005, 2006, 2009 Free Software Foundation, 
Inc.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -15,8 +15,7 @@
    along with this program; if not, write to the Free Software Foundation,
    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
 
-/* Written by Simon Josefsson.  The comments in this file are taken
-   from RFC 2898.  */
+/* Written by Simon Josefsson. */
 
 #include <config.h>
 
@@ -25,32 +24,12 @@
 #include <stdlib.h>
 #include <string.h>
 
-/*
- * 5.2 PBKDF2
- *
- *  PBKDF2 applies a pseudorandom function (see Appendix B.1 for an
- *  example) to derive keys. The length of the derived key is essentially
- *  unbounded. (However, the maximum effective search space for the
- *  derived key may be limited by the structure of the underlying
- *  pseudorandom function. See Appendix B.1 for further discussion.)
- *  PBKDF2 is recommended for new applications.
- *
- *  PBKDF2 (P, S, c, dkLen)
- *
- *  Options:        PRF        underlying pseudorandom function (hLen
- *                             denotes the length in octets of the
- *                             pseudorandom function output)
- *
- *  Input:          P          password, an octet string (ASCII or UTF-8)
- *                  S          salt, an octet string
- *                  c          iteration count, a positive integer
- *                  dkLen      intended length in octets of the derived
- *                             key, a positive integer, at most
- *                             (2^32 - 1) * hLen
- *
- *  Output:         DK         derived key, a dkLen-octet string
- */
-
+/* Implement PKCS#5 PBKDF2 as per RFC 2898.  The PRF to use is hard
+   coded to be HMAC-SHA1.  Inputs are the password P of length PLEN,
+   the salt S of length SLEN, the iteration counter C (> 0), and the
+   desired derived output length DKLEN.  Output buffer is DK which
+   must have room for at least DKLEN octets.  The output buffer will
+   be filled with the derived data.  */
 Gc_rc
 gc_pbkdf2_sha1 (const char *P, size_t Plen,
                const char *S, size_t Slen,
@@ -75,74 +54,12 @@ gc_pbkdf2_sha1 (const char *P, size_t Plen,
   if (dkLen == 0)
     return GC_PKCS5_INVALID_DERIVED_KEY_LENGTH;
 
-  /*
-   *
-   *  Steps:
-   *
-   *     1. If dkLen > (2^32 - 1) * hLen, output "derived key too long" and
-   *        stop.
-   */
-
   if (dkLen > 4294967295U)
     return GC_PKCS5_DERIVED_KEY_TOO_LONG;
 
-  /*
-   *     2. Let l be the number of hLen-octet blocks in the derived key,
-   *        rounding up, and let r be the number of octets in the last
-   *        block:
-   *
-   *                  l = CEIL (dkLen / hLen) ,
-   *                  r = dkLen - (l - 1) * hLen .
-   *
-   *        Here, CEIL (x) is the "ceiling" function, i.e. the smallest
-   *        integer greater than, or equal to, x.
-   */
-
   l = ((dkLen - 1) / hLen) + 1;
   r = dkLen - (l - 1) * hLen;
 
-  /*
-   *     3. For each block of the derived key apply the function F defined
-   *        below to the password P, the salt S, the iteration count c, and
-   *        the block index to compute the block:
-   *
-   *                  T_1 = F (P, S, c, 1) ,
-   *                  T_2 = F (P, S, c, 2) ,
-   *                  ...
-   *                  T_l = F (P, S, c, l) ,
-   *
-   *        where the function F is defined as the exclusive-or sum of the
-   *        first c iterates of the underlying pseudorandom function PRF
-   *        applied to the password P and the concatenation of the salt S
-   *        and the block index i:
-   *
-   *                  F (P, S, c, i) = U_1 \xor U_2 \xor ... \xor U_c
-   *
-   *        where
-   *
-   *                  U_1 = PRF (P, S || INT (i)) ,
-   *                  U_2 = PRF (P, U_1) ,
-   *                  ...
-   *                  U_c = PRF (P, U_{c-1}) .
-   *
-   *        Here, INT (i) is a four-octet encoding of the integer i, most
-   *        significant octet first.
-   *
-   *     4. Concatenate the blocks and extract the first dkLen octets to
-   *        produce a derived key DK:
-   *
-   *                  DK = T_1 || T_2 ||  ...  || T_l<0..r-1>
-   *
-   *     5. Output the derived key DK.
-   *
-   *  Note. The construction of the function F follows a "belt-and-
-   *  suspenders" approach. The iterates U_i are computed recursively to
-   *  remove a degree of parallelism from an opponent; they are exclusive-
-   *  ored together to reduce concerns about the recursion degenerating
-   *  into a small set of values.
-   *
-   */
-
   tmp = malloc (tmplen);
   if (tmp == NULL)
     return GC_MALLOC_ERROR;
-- 
1.6.5.2