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189 lines
6.5 KiB
189 lines
6.5 KiB
From 23f1773ddf92979006d0f438523f3c73320c384f Mon Sep 17 00:00:00 2001
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From: Tomas Mraz <tomas@openssl.org>
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Date: Mon, 28 Feb 2022 18:26:30 +0100
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Subject: [PATCH] Add documentation of BN_mod_sqrt()
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---
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doc/man3/BN_add.pod | 15 +++++++++++++--
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util/missingcrypto.txt | 1 -
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2 files changed, 13 insertions(+), 3 deletions(-)
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diff --git a/doc/man3/BN_add.pod b/doc/man3/BN_add.pod
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index 62d3ee7205..cf6c49c0e3 100644
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--- a/doc/man3/BN_add.pod
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+++ b/doc/man3/BN_add.pod
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@@ -3,7 +3,7 @@
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=head1 NAME
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BN_add, BN_sub, BN_mul, BN_sqr, BN_div, BN_mod, BN_nnmod, BN_mod_add,
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-BN_mod_sub, BN_mod_mul, BN_mod_sqr, BN_exp, BN_mod_exp, BN_gcd -
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+BN_mod_sub, BN_mod_mul, BN_mod_sqr, BN_mod_sqrt, BN_exp, BN_mod_exp, BN_gcd -
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arithmetic operations on BIGNUMs
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=head1 SYNOPSIS
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@@ -36,6 +36,8 @@ arithmetic operations on BIGNUMs
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int BN_mod_sqr(BIGNUM *r, BIGNUM *a, const BIGNUM *m, BN_CTX *ctx);
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+ BIGNUM *BN_mod_sqrt(BIGNUM *in, BIGNUM *a, const BIGNUM *p, BN_CTX *ctx);
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+
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int BN_exp(BIGNUM *r, BIGNUM *a, BIGNUM *p, BN_CTX *ctx);
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int BN_mod_exp(BIGNUM *r, BIGNUM *a, const BIGNUM *p,
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@@ -87,6 +89,12 @@ L<BN_mod_mul_reciprocal(3)>.
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BN_mod_sqr() takes the square of I<a> modulo B<m> and places the
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result in I<r>.
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+BN_mod_sqrt() returns the modular square root of I<a> such that
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+C<in^2 = a (mod p)>. The modulus I<p> must be a
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+prime, otherwise an error or an incorrect "result" will be returned.
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+The result is stored into I<in> which can be NULL. The result will be
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+newly allocated in that case.
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+
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BN_exp() raises I<a> to the I<p>-th power and places the result in I<r>
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(C<r=a^p>). This function is faster than repeated applications of
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BN_mul().
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@@ -108,7 +116,10 @@ the arguments.
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=head1 RETURN VALUES
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-For all functions, 1 is returned for success, 0 on error. The return
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+The BN_mod_sqrt() returns the result (possibly incorrect if I<p> is
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+not a prime), or NULL.
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+
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+For all remaining functions, 1 is returned for success, 0 on error. The return
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value should always be checked (e.g., C<if (!BN_add(r,a,b)) goto err;>).
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The error codes can be obtained by L<ERR_get_error(3)>.
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diff --git a/util/missingcrypto.txt b/util/missingcrypto.txt
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index b61bdeb880..4d2fd7f6b7 100644
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--- a/util/missingcrypto.txt
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+++ b/util/missingcrypto.txt
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@@ -264,7 +264,6 @@ BN_mod_lshift(3)
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BN_mod_lshift1(3)
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BN_mod_lshift1_quick(3)
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BN_mod_lshift_quick(3)
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-BN_mod_sqrt(3)
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BN_mod_sub_quick(3)
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BN_nist_mod_192(3)
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BN_nist_mod_224(3)
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From 46673310c9a755b2a56f53d115854983d6ada11a Mon Sep 17 00:00:00 2001
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From: Tomas Mraz <tomas@openssl.org>
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Date: Mon, 28 Feb 2022 18:26:35 +0100
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Subject: [PATCH] Add a negative testcase for BN_mod_sqrt
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---
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test/bntest.c | 11 ++++++++++-
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test/recipes/10-test_bn_data/bnmod.txt | 12 ++++++++++++
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2 files changed, 22 insertions(+), 1 deletion(-)
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diff --git a/test/bntest.c b/test/bntest.c
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index efdb3ef963..d49f87373a 100644
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--- a/test/bntest.c
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+++ b/test/bntest.c
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@@ -1732,8 +1732,17 @@ static int file_modsqrt(STANZA *s)
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|| !TEST_ptr(ret2 = BN_new()))
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goto err;
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+ if (BN_is_negative(mod_sqrt)) {
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+ /* A negative testcase */
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+ if (!TEST_ptr_null(BN_mod_sqrt(ret, a, p, ctx)))
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+ goto err;
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+
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+ st = 1;
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+ goto err;
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+ }
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+
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/* There are two possible answers. */
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- if (!TEST_true(BN_mod_sqrt(ret, a, p, ctx))
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+ if (!TEST_ptr(BN_mod_sqrt(ret, a, p, ctx))
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|| !TEST_true(BN_sub(ret2, p, ret)))
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goto err;
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diff --git a/test/recipes/10-test_bn_data/bnmod.txt b/test/recipes/10-test_bn_data/bnmod.txt
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index e22d656091..bc8a434ea5 100644
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--- a/test/recipes/10-test_bn_data/bnmod.txt
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+++ b/test/recipes/10-test_bn_data/bnmod.txt
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@@ -2799,3 +2799,15 @@ P = 9df9d6cc20b8540411af4e5357ef2b0353cb1f2ab5ffc3e246b41c32f71e951f
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ModSqrt = a1d52989f12f204d3d2167d9b1e6c8a6174c0c786a979a5952383b7b8bd186
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A = 2eee37cf06228a387788188e650bc6d8a2ff402931443f69156a29155eca07dcb45f3aac238d92943c0c25c896098716baa433f25bd696a142f5a69d5d937e81
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P = 9df9d6cc20b8540411af4e5357ef2b0353cb1f2ab5ffc3e246b41c32f71e951f
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+
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+# Negative testcases for BN_mod_sqrt()
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+
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+# This one triggers an infinite loop with unfixed implementation
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+# It should just fail.
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+ModSqrt = -1
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+A = 20a7ee
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+P = 460201
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+
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+ModSqrt = -1
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+A = 65bebdb00a96fc814ec44b81f98b59fba3c30203928fa5214c51e0a97091645280c947b005847f239758482b9bfc45b066fde340d1fe32fc9c1bf02e1b2d0ed
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+P = 9df9d6cc20b8540411af4e5357ef2b0353cb1f2ab5ffc3e246b41c32f71e951f
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From cafcc62d7719dea73f334c9ef763d1e215fcd94d Mon Sep 17 00:00:00 2001
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From: Tomas Mraz <tomas@openssl.org>
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Date: Mon, 28 Feb 2022 18:26:21 +0100
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Subject: [PATCH] Fix possible infinite loop in BN_mod_sqrt()
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The calculation in some cases does not finish for non-prime p.
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This fixes CVE-2022-0778.
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Based on patch by David Benjamin <davidben@google.com>.
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---
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crypto/bn/bn_sqrt.c | 30 ++++++++++++++++++------------
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1 file changed, 18 insertions(+), 12 deletions(-)
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diff --git a/crypto/bn/bn_sqrt.c b/crypto/bn/bn_sqrt.c
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index b663ae5ec5..c5ea7ab194 100644
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--- a/crypto/bn/bn_sqrt.c
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+++ b/crypto/bn/bn_sqrt.c
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@@ -14,7 +14,8 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
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/*
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* Returns 'ret' such that ret^2 == a (mod p), using the Tonelli/Shanks
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* algorithm (cf. Henri Cohen, "A Course in Algebraic Computational Number
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- * Theory", algorithm 1.5.1). 'p' must be prime!
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+ * Theory", algorithm 1.5.1). 'p' must be prime, otherwise an error or
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+ * an incorrect "result" will be returned.
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*/
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{
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BIGNUM *ret = in;
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@@ -303,18 +304,23 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
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goto vrfy;
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}
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- /* find smallest i such that b^(2^i) = 1 */
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- i = 1;
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- if (!BN_mod_sqr(t, b, p, ctx))
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- goto end;
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- while (!BN_is_one(t)) {
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- i++;
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- if (i == e) {
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- ERR_raise(ERR_LIB_BN, BN_R_NOT_A_SQUARE);
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- goto end;
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+ /* Find the smallest i, 0 < i < e, such that b^(2^i) = 1. */
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+ for (i = 1; i < e; i++) {
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+ if (i == 1) {
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+ if (!BN_mod_sqr(t, b, p, ctx))
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+ goto end;
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+
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+ } else {
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+ if (!BN_mod_mul(t, t, t, p, ctx))
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+ goto end;
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}
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- if (!BN_mod_mul(t, t, t, p, ctx))
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- goto end;
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+ if (BN_is_one(t))
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+ break;
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+ }
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+ /* If not found, a is not a square or p is not prime. */
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+ if (i >= e) {
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+ ERR_raise(ERR_LIB_BN, BN_R_NOT_A_SQUARE);
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+ goto end;
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}
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/* t := y^2^(e - i - 1) */
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