gpgsm: decrypting session key failed: Invalid session key

[Henning Schild]

Hi,

this is a bug report email, at least i expect it is a bug.

An increasing amount of x509 encrypted email i receive can not be
decrypted with gpgsm anymore. At first i assumed that the senders keys
would be somehow different and trigger the bug in gpgsm. Later i found
that it could also be their mail client, but whatever it is on the remote
end i expect it to be a bug in gpgsm.
The same files can be decrypted with openssl just fine.

Affected versions: gpgsm <= latest master (gnupg-2.2.7-609-g4195ce15f)
Platform Linux: x86_64

Expected result:
Mail can be decrypted and read.

Actual result:
Decryption fails with "gpgsm: decrypting session key failed: Invalid
session key"

Details: (from latest git build)
$ /foo/gnupg/sm/gpgsm --debug-level guru --decrypt smime_bad.p7m
...
gpgsm: DBG: chan_5 -> PKDECRYPT
gpgsm: DBG: chan_5 <- S INQUIRE_MAXLEN 4096
gpgsm: DBG: chan_5 <- INQUIRE CIPHERTEXT
gpgsm: DBG: chan_5 -> [ 44 20 28 37 3a 65 6e 63 2d 76 61 6c 28 33 3a 72 ...(273 byte(s) skipped) ]
gpgsm: DBG: chan_5 -> END
Vim: Reading from stdin...
gpgsm: DBG: chan_5 <- S PADDING 0
gpgsm: DBG: chan_5 <- [ 44 20 28 35 3a 76 61 6c 75 65 33 32 3a e5 ff cd ...(31 byte(s) skipped) ]
gpgsm: DBG: chan_5 <- OK
gpgsm: DBG: pkcs1 encoded session key: e5ffcd51107897682fc0d805173d85ce7088fddabda33ac74da73b0813c04593
gpgsm: decrypting session key failed: Invalid session key
gpgsm: message decryption failed: Invalid session key <GpgSM>


Hope that helps. I would be happy to provide more information. I have
many of those _bad.p7m files.

regards,
Henning