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EAP-pwd: Fix zero-padding of input to H()

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Another niceness of OpenSSL is that if the high-order bit of a 521-bit
big num is not set then BN_bn2bin() will just return 65 bytes instead of
66 bytes with the 1st (big endian, after all) being all zero. When this
happens the wrong number of octets are mixed into function H(). So
there's a whole bunch of "offset" computations and BN_bn2bin() dumps the
big number into a buffer + offset. That should be obvious in the patch
too.
This commit is contained in:
Dan Harkins 2011-11-19 16:47:25 +02:00 • committed by Jouni Malinen
parent 18f5f3de03
commit e547e071e1
3 changed files with 76 additions and 31 deletions
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12
src/eap_common/eap_pwd_common.c
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@ -284,6 +284,7 @@ int compute_keys(EAP_PWD_group *grp, BN_CTX *bnctx, BIGNUM *k,
u8 mk[SHA256_DIGEST_LENGTH], *cruft;
u8 session_id[SHA256_DIGEST_LENGTH + 1];
u8 msk_emsk[EAP_MSK_LEN + EAP_EMSK_LEN];
int offset;
if ((cruft = os_malloc(BN_num_bytes(grp->prime))) == NULL)
return -1;
@ -295,16 +296,21 @@ int compute_keys(EAP_PWD_group *grp, BN_CTX *bnctx, BIGNUM *k,
session_id[0] = EAP_TYPE_PWD;
H_Init(&ctx);
H_Update(&ctx, (u8 *)ciphersuite, sizeof(u32));
BN_bn2bin(peer_scalar, cruft);
offset = BN_num_bytes(grp->order) - BN_num_bytes(peer_scalar);
os_memset(cruft, 0, BN_num_bytes(grp->prime));
BN_bn2bin(peer_scalar, cruft + offset);
H_Update(&ctx, cruft, BN_num_bytes(grp->order));
BN_bn2bin(server_scalar, cruft);
offset = BN_num_bytes(grp->order) - BN_num_bytes(server_scalar);
os_memset(cruft, 0, BN_num_bytes(grp->prime));
BN_bn2bin(server_scalar, cruft + offset);
H_Update(&ctx, cruft, BN_num_bytes(grp->order));
H_Final(&ctx, &session_id[1]);
/* then compute MK = H(k | commit-peer | commit-server) */
H_Init(&ctx);
offset = BN_num_bytes(grp->prime) - BN_num_bytes(k);
os_memset(cruft, 0, BN_num_bytes(grp->prime));
BN_bn2bin(k, cruft);
BN_bn2bin(k, cruft + offset);
H_Update(&ctx, cruft, BN_num_bytes(grp->prime));
H_Update(&ctx, commit_peer, SHA256_DIGEST_LENGTH);
H_Update(&ctx, commit_server, SHA256_DIGEST_LENGTH);