From 302d38e3f73d5fd2ba2fd30bb7798778cb9f18dd Mon Sep 17 00:00:00 2001 From: Matt Caswell Date: Thu, 26 Feb 2015 13:52:30 +0000 Subject: [PATCH] Deprecate RAND_pseudo_bytes The justification for RAND_pseudo_bytes is somewhat dubious, and the reality is that it is frequently being misused. RAND_bytes and RAND_pseudo_bytes in the default implementation both end up calling ssleay_rand_bytes. Both may return -1 in an error condition. If there is insufficient entropy then both will return 0, but RAND_bytes will additionally add an error to the error queue. They both return 1 on success. Therefore the fundamental difference between the two is that one will add an error to the error queue with insufficient entory whilst the other will not. Frequently there are constructions of this form: if(RAND_pseudo_bytes(...) <= 1) goto err; In the above form insufficient entropy is treated as an error anyway, so RAND_bytes is probably the better form to use. This form is also seen: if(!RAND_pseudo_bytes(...)) goto err; This is technically not correct at all since a -1 return value is incorrectly handled - but this form will also treat insufficient entropy as an error. Within libssl it is required that you have correctly seeded your entropy pool and so there seems little benefit in using RAND_pseudo_bytes. Similarly in libcrypto many operations also require a correctly seeded entropy pool and so in most interesting cases you would be better off using RAND_bytes anyway. There is a significant risk of RAND_pseudo_bytes being incorrectly used in scenarios where security can be compromised by insufficient entropy. If you are not using the default implementation, then most engines use the same function to implement RAND_bytes and RAND_pseudo_bytes in any case. Given its misuse, limited benefit, and potential to compromise security, RAND_pseudo_bytes has been deprecated. Reviewed-by: Richard Levitte --- CHANGES | 2 ++ crypto/rand/md_rand.c | 8 ++++++++ crypto/rand/rand.h | 4 +++- crypto/rand/rand_lib.c | 2 ++ doc/crypto/RAND_bytes.pod | 3 +++ 5 files changed, 18 insertions(+), 1 deletion(-) diff --git a/CHANGES b/CHANGES index ab5b48250c..7c57410a73 100644 --- a/CHANGES +++ b/CHANGES @@ -4,6 +4,8 @@ Changes between 1.0.2 and 1.1.0 [xx XXX xxxx] + *) RAND_pseudo_bytes has been deprecated. Users should use RAND bytes instead. + *) Added support for TLS extended master secret from draft-ietf-tls-session-hash-03.txt. Thanks for Alfredo Pironti for an initial patch which was a great help during development. diff --git a/crypto/rand/md_rand.c b/crypto/rand/md_rand.c index ef43966814..27e785d311 100644 --- a/crypto/rand/md_rand.c +++ b/crypto/rand/md_rand.c @@ -173,7 +173,9 @@ static int ssleay_rand_seed(const void *buf, int num); static int ssleay_rand_add(const void *buf, int num, double add_entropy); static int ssleay_rand_bytes(unsigned char *buf, int num, int pseudo); static int ssleay_rand_nopseudo_bytes(unsigned char *buf, int num); +#ifndef OPENSSL_NO_DEPRECATED static int ssleay_rand_pseudo_bytes(unsigned char *buf, int num); +#endif static int ssleay_rand_status(void); static RAND_METHOD rand_ssleay_meth = { @@ -181,7 +183,11 @@ static RAND_METHOD rand_ssleay_meth = { ssleay_rand_nopseudo_bytes, ssleay_rand_cleanup, ssleay_rand_add, +#ifndef OPENSSL_NO_DEPRECATED ssleay_rand_pseudo_bytes, +#else + NULL, +#endif ssleay_rand_status }; @@ -601,6 +607,7 @@ static int ssleay_rand_nopseudo_bytes(unsigned char *buf, int num) return ssleay_rand_bytes(buf, num, 0); } +#ifndef OPENSSL_NO_DEPRECATED /* * pseudo-random bytes that are guaranteed to be unique but not unpredictable */ @@ -608,6 +615,7 @@ static int ssleay_rand_pseudo_bytes(unsigned char *buf, int num) { return ssleay_rand_bytes(buf, num, 1); } +#endif static int ssleay_rand_status(void) { diff --git a/crypto/rand/rand.h b/crypto/rand/rand.h index 145edb2d8f..14b479343a 100644 --- a/crypto/rand/rand.h +++ b/crypto/rand/rand.h @@ -95,7 +95,9 @@ int RAND_set_rand_engine(ENGINE *engine); RAND_METHOD *RAND_SSLeay(void); void RAND_cleanup(void); int RAND_bytes(unsigned char *buf, int num); -int RAND_pseudo_bytes(unsigned char *buf, int num); +#ifdef OPENSSL_USE_DEPRECATED +DECLARE_DEPRECATED(int RAND_pseudo_bytes(unsigned char *buf, int num)); +#endif void RAND_seed(const void *buf, int num); void RAND_add(const void *buf, int num, double entropy); int RAND_load_file(const char *file, long max_bytes); diff --git a/crypto/rand/rand_lib.c b/crypto/rand/rand_lib.c index 2f4dc09155..0bbaf675e2 100644 --- a/crypto/rand/rand_lib.c +++ b/crypto/rand/rand_lib.c @@ -159,6 +159,7 @@ int RAND_bytes(unsigned char *buf, int num) return (-1); } +#ifndef OPENSSL_NO_DEPRECATED int RAND_pseudo_bytes(unsigned char *buf, int num) { const RAND_METHOD *meth = RAND_get_rand_method(); @@ -166,6 +167,7 @@ int RAND_pseudo_bytes(unsigned char *buf, int num) return meth->pseudorand(buf, num); return (-1); } +#endif int RAND_status(void) { diff --git a/doc/crypto/RAND_bytes.pod b/doc/crypto/RAND_bytes.pod index 1a9b91e281..f3a5ed22f8 100644 --- a/doc/crypto/RAND_bytes.pod +++ b/doc/crypto/RAND_bytes.pod @@ -10,6 +10,8 @@ RAND_bytes, RAND_pseudo_bytes - generate random data int RAND_bytes(unsigned char *buf, int num); +Deprecated: + int RAND_pseudo_bytes(unsigned char *buf, int num); =head1 DESCRIPTION @@ -18,6 +20,7 @@ RAND_bytes() puts B cryptographically strong pseudo-random bytes into B. An error occurs if the PRNG has not been seeded with enough randomness to ensure an unpredictable byte sequence. +RAND_pseudo_bytes() has been deprecated. Users should use RAND_bytes() instead. RAND_pseudo_bytes() puts B pseudo-random bytes into B. Pseudo-random byte sequences generated by RAND_pseudo_bytes() will be unique if they are of sufficient length, but are not necessarily -- 2.25.1