Updated per comments from @gilles-peskine-arm.
Signed-off-by: stroebeljc <stroebeljc1@gmail.com>
diff --git a/ChangeLog.d/issue3819.txt b/ChangeLog.d/issue3819.txt
index 927b6a2..7723c65 100644
--- a/ChangeLog.d/issue3819.txt
+++ b/ChangeLog.d/issue3819.txt
@@ -1,4 +1,5 @@
-Bugfix
- * Fix incorrect seed generation when a nonce is included
- in mbedtls_ctr_drbg_reseed_internal.
+Security
+ * Fix a security reduction error that caused all bits of the nonce
+ to be zero in mbedtls_ctr_drbg_reseed_internal. This prevented
+ the security strength from reaching the level required by NIST.
Found by John Stroebel in #3819 and fixed in #3973.
diff --git a/library/ctr_drbg.c b/library/ctr_drbg.c
index 7958041..3815dc7 100644
--- a/library/ctr_drbg.c
+++ b/library/ctr_drbg.c
@@ -724,11 +724,11 @@
0x4a, 0x47, 0xc2, 0xf3, 0x85, 0x16, 0xb4, 0x6f,
0x00, 0x2e, 0x71, 0xda, 0xed, 0x16, 0x9b, 0x5c };
-static const unsigned char nonce_pers_pr[] =
+static const unsigned char pers_pr[] =
{ 0xbf, 0xa4, 0x9a, 0x8f, 0x7b, 0xd8, 0xb1, 0x7a,
0x9d, 0xfa, 0x45, 0xed, 0x21, 0x52, 0xb3, 0xad };
-static const unsigned char nonce_pers_nopr[] =
+static const unsigned char pers_nopr[] =
{ 0x4e, 0x61, 0x79, 0xd4, 0xc2, 0x72, 0xa1, 0x4c,
0xf1, 0x3d, 0xf6, 0x5e, 0xa3, 0xa6, 0xe5, 0x0f };
@@ -781,13 +781,13 @@
0x4f, 0x11, 0xa6, 0x86, 0x51, 0xf2, 0x3e, 0x3a,
0x8b, 0x1f, 0xdc, 0x03, 0xb1, 0x92, 0xc7, 0xe7 };
-static const unsigned char nonce_pers_pr[] =
+static const unsigned char pers_pr[] =
{ 0x5a, 0x70, 0x95, 0xe9, 0x81, 0x40, 0x52, 0x33,
0x91, 0x53, 0x7e, 0x75, 0xd6, 0x19, 0x9d, 0x1e,
0xad, 0x0d, 0xc6, 0xa7, 0xde, 0x6c, 0x1f, 0xe0,
0xea, 0x18, 0x33, 0xa8, 0x7e, 0x06, 0x20, 0xe9 };
-static const unsigned char nonce_pers_nopr[] =
+static const unsigned char pers_nopr[] =
{ 0x88, 0xee, 0xb8, 0xe0, 0xe8, 0x3b, 0xf3, 0x29,
0x4b, 0xda, 0xcd, 0x60, 0x99, 0xeb, 0xe4, 0xbf,
0x55, 0xec, 0xd9, 0x11, 0x3f, 0x71, 0xe5, 0xeb,
@@ -831,13 +831,15 @@
return( 1 ); \
}
+#define SELF_TEST_OUPUT_DISCARD_LENGTH 64
+
/*
* Checkup routine
*/
int mbedtls_ctr_drbg_self_test( int verbose )
{
mbedtls_ctr_drbg_context ctx;
- unsigned char buf[64];
+ unsigned char buf[ sizeof( result_pr ) ];
mbedtls_ctr_drbg_init( &ctx );
@@ -849,15 +851,15 @@
test_offset = 0;
mbedtls_ctr_drbg_set_entropy_len( &ctx, MBEDTLS_CTR_DRBG_KEYSIZE );
- mbedtls_ctr_drbg_set_nonce_len( &ctx, MBEDTLS_CTR_DRBG_KEYSIZE >> 1 );
+ mbedtls_ctr_drbg_set_nonce_len( &ctx, MBEDTLS_CTR_DRBG_KEYSIZE / 2 );
CHK( mbedtls_ctr_drbg_seed( &ctx,
ctr_drbg_self_test_entropy,
(void *) entropy_source_pr,
- nonce_pers_pr, MBEDTLS_CTR_DRBG_KEYSIZE ) );
+ pers_pr, MBEDTLS_CTR_DRBG_KEYSIZE ) );
mbedtls_ctr_drbg_set_prediction_resistance( &ctx, MBEDTLS_CTR_DRBG_PR_ON );
- CHK( mbedtls_ctr_drbg_random( &ctx, buf, 64 ) );
- CHK( mbedtls_ctr_drbg_random( &ctx, buf, 64 ) );
- CHK( memcmp( buf, result_pr, 64 ) );
+ CHK( mbedtls_ctr_drbg_random( &ctx, buf, SELF_TEST_OUPUT_DISCARD_LENGTH ) );
+ CHK( mbedtls_ctr_drbg_random( &ctx, buf, sizeof( result_pr ) ) );
+ CHK( memcmp( buf, result_pr, sizeof( result_pr ) ) );
mbedtls_ctr_drbg_free( &ctx );
@@ -874,15 +876,15 @@
test_offset = 0;
mbedtls_ctr_drbg_set_entropy_len( &ctx, MBEDTLS_CTR_DRBG_KEYSIZE);
- mbedtls_ctr_drbg_set_nonce_len( &ctx, MBEDTLS_CTR_DRBG_KEYSIZE >> 1 );
+ mbedtls_ctr_drbg_set_nonce_len( &ctx, MBEDTLS_CTR_DRBG_KEYSIZE / 2 );
CHK( mbedtls_ctr_drbg_seed( &ctx,
ctr_drbg_self_test_entropy,
(void *) entropy_source_nopr,
- nonce_pers_nopr, MBEDTLS_CTR_DRBG_KEYSIZE ) );
+ pers_nopr, MBEDTLS_CTR_DRBG_KEYSIZE ) );
CHK( mbedtls_ctr_drbg_reseed( &ctx, NULL, 0 ) );
- CHK( mbedtls_ctr_drbg_random( &ctx, buf, 64 ) );
- CHK( mbedtls_ctr_drbg_random( &ctx, buf, 64 ) );
- CHK( memcmp( buf, result_nopr, 64 ) );
+ CHK( mbedtls_ctr_drbg_random( &ctx, buf, SELF_TEST_OUPUT_DISCARD_LENGTH ) );
+ CHK( mbedtls_ctr_drbg_random( &ctx, buf, sizeof( result_nopr ) ) );
+ CHK( memcmp( buf, result_nopr, sizeof( result_nopr ) ) );
mbedtls_ctr_drbg_free( &ctx );