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gpg: Be prepared for chosen-prefix SHA-1 collisions in key signatures.

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* g10/sig-check.c (check_signature_over_key_or_uid): Reject cewrtain
SHA-1 based signatures.
--

Signed-off-by: Werner Koch <wk@gnupg.org>
This commit is contained in:
Werner Koch 2019-10-03 17:43:26 +02:00
parent 63dbc817e7
commit c4f2d9e3e1
No known key found for this signature in database
GPG Key ID: E3FDFF218E45B72B
1 changed files with 29 additions and 15 deletions
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44
g10/sig-check.c
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@ -871,6 +871,10 @@ check_signature_over_key_or_uid (ctrl_t ctrl, PKT_public_key *signer,
PKT_public_key *pripk = kb->pkt->pkt.public_key; PKT_public_key *pripk = kb->pkt->pkt.public_key;
gcry_md_hd_t md; gcry_md_hd_t md;
int signer_alloced = 0; int signer_alloced = 0;
int stub_is_selfsig;
if (!is_selfsig)
is_selfsig = &stub_is_selfsig;
rc = openpgp_pk_test_algo (sig->pubkey_algo); rc = openpgp_pk_test_algo (sig->pubkey_algo);
if (rc) if (rc)
@ -904,14 +908,11 @@ check_signature_over_key_or_uid (ctrl_t ctrl, PKT_public_key *signer,
if (signer) if (signer)
{ {
if (is_selfsig) if (signer->keyid[0] == pripk->keyid[0]
{ && signer->keyid[1] == pripk->keyid[1])
if (signer->keyid[0] == pripk->keyid[0] *is_selfsig = 1;
&& signer->keyid[1] == pripk->keyid[1]) else
*is_selfsig = 1; *is_selfsig = 0;
else
*is_selfsig = 0;
}
} }
else else
{ {
@ -921,8 +922,7 @@ check_signature_over_key_or_uid (ctrl_t ctrl, PKT_public_key *signer,
{ {
/* Issued by the primary key. */ /* Issued by the primary key. */
signer = pripk; signer = pripk;
if (is_selfsig) *is_selfsig = 1;
*is_selfsig = 1;
} }
else else
{ {
@ -951,8 +951,7 @@ check_signature_over_key_or_uid (ctrl_t ctrl, PKT_public_key *signer,
if (! signer) if (! signer)
{ {
/* Signer by some other key. */ /* Signer by some other key. */
if (is_selfsig) *is_selfsig = 0;
*is_selfsig = 0;
if (ret_pk) if (ret_pk)
{ {
signer = ret_pk; signer = ret_pk;
@ -1013,9 +1012,24 @@ check_signature_over_key_or_uid (ctrl_t ctrl, PKT_public_key *signer,
else if (IS_UID_SIG (sig) || IS_UID_REV (sig)) else if (IS_UID_SIG (sig) || IS_UID_REV (sig))
{ {
log_assert (packet->pkttype == PKT_USER_ID); log_assert (packet->pkttype == PKT_USER_ID);
hash_public_key (md, pripk); log_debug ("algo=%d selfsig=%d tm=%lu\n",
hash_uid_packet (packet->pkt.user_id, md, sig); sig->digest_algo, *is_selfsig, (unsigned long)sig->timestamp);
rc = check_signature_end_simple (signer, sig, md, NULL, 0); if (sig->digest_algo == DIGEST_ALGO_SHA1 && !*is_selfsig
&& sig->timestamp > 1547856000)
{
/* If the signature was created using SHA-1 we consider this
* signature invalid because it makes it possible to mount a
* chosen-prefix collision. We don't do this for
* self-signatures or for signatures created before the
* somewhat arbitrary cut-off date 2019-01-19. */
rc = gpg_error (GPG_ERR_DIGEST_ALGO);
}
else
{
hash_public_key (md, pripk);
hash_uid_packet (packet->pkt.user_id, md, sig);
rc = check_signature_end_simple (signer, sig, md, NULL, 0);
}
} }
else else
{ {