pkinit: Correctly pad Diffie-Hellman key #1177
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If the Diffie-Hellman key was ‘n’ bytes too short, we would shift it to the right ‘n’ places, padding it out to the correct length to compute the reply key. Unfortunately, we forgot to increase the size of the key accordingly, so ‘n’ trailing key bytes would be discarded. This could mean failure to decrypt a reply when interoperating with a Kerberos implementation without this bug. Signed-off-by: Joseph Sutton <[email protected]>
abartlet
reviewed
Nov 2, 2023
| @@ -230,6 +230,7 @@ generate_dh_keyblock(krb5_context context, | |||
| size -= dh_gen_keylen; | |||
| memmove(dh_gen_key + size, dh_gen_key, dh_gen_keylen); | |||
| memset(dh_gen_key, 0, size); | |||
| dh_gen_keylen += size; | |||
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Does the buggy client mean we need to try both possibilities now?
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Yes, if we want to interoperate with buggy Heimdal clients without sporadic failures. For the other way round, interoperating with buggy Heimdal servers, the client probably would need to keep regenerating the key until it got a working one.
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Does the existing code successfully interoperate with MIT?
I don’t know. I haven’t tested that.
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The client side of this patch seems to have fixed client side pkinit failures we were seeing against an AD KDC. |
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If the Diffie-Hellman key was ‘n’ bytes too short, we would shift it to the right ‘n’ places, padding it out to the correct length to compute the reply key.
Unfortunately, we forgot to increase the size of the key accordingly, so ‘n’ trailing key bytes would be discarded. This could mean failure to decrypt a reply when interoperating with a Kerberos implementation without this bug.