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Work around DSA formatting bug in commercial-SSH 2.0.13

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[originally from svn r665]
This commit is contained in:
Simon Tatham 2000-10-03 09:05:56 +00:00
parent e9caa5e3b6
commit 01ca2d8077
1 changed files with 17 additions and 4 deletions
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21
sshdss.c
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@ -161,11 +161,24 @@ static int dss_verifysig(char *sig, int siglen, char *data, int datalen) {
if (!dss_p)
return 0;
getstring(&sig, &siglen, &p, &slen);
if (!p || memcmp(p, "ssh-dss", 7)) {
return 0;
/*
* Commercial SSH (2.0.13) and OpenSSH disagree over the format
* of a DSA signature. OpenSSH is in line with the IETF drafts:
* it uses a string "ssh-dss", followed by a 40-byte string
* containing two 160-bit integers end-to-end. Commercial SSH
* can't be bothered with the header bit, and considers a DSA
* signature blob to be _just_ the 40-byte string containing
* the two 160-bit integers. We tell them apart by measuring
* the length: length 40 means the commercial-SSH bug, anything
* else is assumed to be IETF-compliant.
*/
if (siglen != 40) { /* bug not present; read admin fields */
getstring(&sig, &siglen, &p, &slen);
if (!p || memcmp(p, "ssh-dss", 7)) {
return 0;
}
sig += 4, siglen -= 4; /* skip yet another length field */
}
sig += 4, siglen -= 4; /* skip yet another length field */
r = get160(&sig, &siglen);
s = get160(&sig, &siglen);
if (!r || !s)