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Fix mpint signedness bug in importing PEM ECDSA keys.

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The OpenSSH PEM format contains a big integer with the top bit
potentially set, which we handle by copying the data into a faked up
instance of our own private key format, and passing that to
ecdsa_createkey(). But our own private key format expects an SSH-2
standard mpint, i.e. with the top bit reliably clear, so this might
fail for no good reason.

Fixed by prefixing a zero byte unconditionally when constructing the
fake private blob.
This commit is contained in:
Simon Tatham 2015-05-15 14:01:35 +01:00
parent 8dab2c2440
commit dee305c318
1 changed files with 12 additions and 4 deletions
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16
import.c
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@ -753,7 +753,7 @@ struct ssh2_userkey *openssh_pem_read(const Filename *filename,
goto error;
}
retkey->alg = alg;
blob = snewn((4+19 + 4+8 + 4+len) + (4+privlen), unsigned char);
blob = snewn((4+19 + 4+8 + 4+len) + (4+1+privlen), unsigned char);
if (!blob) {
sfree(retkey);
errmsg = "out of memory";
@ -773,12 +773,20 @@ struct ssh2_userkey *openssh_pem_read(const Filename *filename,
PUT_32BIT(q, len); q += 4;
memcpy(q, p, len); q += len;
PUT_32BIT(q, privlen);
memcpy(q+4, priv, privlen);
/*
* To be acceptable to our createkey(), the private blob must
* contain a valid mpint, i.e. without the top bit set. But
* the input private string may have the top bit set, so we
* prefix a zero byte to ensure createkey() doesn't fail for
* that reason.
*/
PUT_32BIT(q, privlen+1);
q[4] = 0;
memcpy(q+5, priv, privlen);
retkey->data = retkey->alg->createkey(retkey->alg,
blob, q-blob,
q, 4+privlen);
q, 5+privlen);
if (!retkey->data) {
sfree(retkey);