Cannot decrypt file encrypted with enQsig

[Felix E. Klee]

Hi Dirk,

thanks for all your suggestions!

If I can, I want to avoid creating another key. I prefer getting the
issue resolved and have bugs reported/fixed along the way. I had it once
before that I could not decrypt a document encrypted by a big German
company with my private key. These enterprise “solutions” seem to have
issues.

On Mon, Jul 30, 2018 at 5:14 PM, Dirk Gottschalk via Gnupg-users
<gnupg-users at gnupg.org> wrote:
> The last packet mentions your signature key as used for encryption,
> this is an error for sure.

I now removed my signature key BEF6EFD38FE8DCA0 from the encrypted
message:

    $ gpg --dearmor encrypted.asc
    $ gpgsplit encrypted.asc.gpg
    $ ls -1
    000001-001.pk_enc
    000002-001.pk_enc
    000003-001.pk_enc
    000004-001.pk_enc
    000005-018.encrypted_mdc
    encrypted.asc
    encrypted.asc.gpg
    $ pgpdump 000001-001.pk_enc
    New: Public-Key Encrypted Session Key Packet(tag 1)(524 bytes)
            New version(3)
            Key ID - 0xBEF6EFD38FE8DCA0
            Pub alg - RSA Encrypt or Sign(pub 1)
            RSA m^e mod n(4096 bits) - ...
                    -> m = sym alg(1 byte) + checksum(2 bytes) + PKCS-1
    block type 02
    $ pgpdump 000002-001.pk_enc
    New: Public-Key Encrypted Session Key Packet(tag 1)(524 bytes)
            New version(3)
            Key ID - 0x04FDF78D1679DD94
            Pub alg - RSA Encrypt or Sign(pub 1)
            RSA m^e mod n(4095 bits) - ...
                    -> m = sym alg(1 byte) + checksum(2 bytes) + PKCS-1
    block type 02
    $ pgpdump 000003-001.pk_enc
    New: Public-Key Encrypted Session Key Packet(tag 1)(524 bytes)
            New version(3)
            Key ID - 0x92663E7CA68E4EC6
            Pub alg - RSA Encrypt or Sign(pub 1)
            RSA m^e mod n(4096 bits) - ...
                    -> m = sym alg(1 byte) + checksum(2 bytes) + PKCS-1
    block type 02
    $ pgpdump 000004-001.pk_enc
    New: Public-Key Encrypted Session Key Packet(tag 1)(524 bytes)
            New version(3)
            Key ID - 0x9D8C454A43A6D2DE
            Pub alg - RSA Encrypt or Sign(pub 1)
            RSA m^e mod n(4094 bits) - ...
                    -> m = sym alg(1 byte) + checksum(2 bytes) + PKCS-1
    block type 02
    $ pgpdump 000005-018.encrypted_mdc
    New: Symmetrically Encrypted and MDC Packet(tag 18)(1718 bytes)
            Ver 1
                    (plain text + MDC SHA1(20 bytes))
    $ cat 000002-001.pk_enc 000003-001.pk_enc 000004-001.pk_enc \
    000005-018.encrypted_mdc >new.gpg

Decryption still fails:

    $ gpg -d new.gpg
    gpg: encrypted with RSA key, ID 9D8C454A43A6D2DE
    gpg: encrypted with RSA key, ID 92663E7CA68E4EC6
    gpg: encrypted with 4096-bit RSA key, ID 04FDF78D1679DD94, created
    2016-12-17
          "Felix E. Klee <felix.klee at inka.de>"
    gpg: public key decryption failed: Missing item in object
    gpg: decryption failed: No secret key
    $ gpg --list-packets new.gpg
    gpg: encrypted with RSA key, ID 9D8C454A43A6D2DE
    gpg: encrypted with RSA key, ID 92663E7CA68E4EC6
    gpg: encrypted with 4096-bit RSA key, ID 04FDF78D1679DD94, created
    2016-12-17
          "Felix E. Klee <felix.klee at inka.de>"
    gpg: public key decryption failed: Missing item in object
    gpg: decryption failed: No secret key
    # off=0 ctb=c1 tag=1 hlen=3 plen=524 new-ctb
    :pubkey enc packet: version 3, algo 1, keyid 04FDF78D1679DD94
    data: [4095 bits]
    # off=527 ctb=c1 tag=1 hlen=3 plen=524 new-ctb
    :pubkey enc packet: version 3, algo 1, keyid 92663E7CA68E4EC6
    data: [4096 bits]
    # off=1054 ctb=c1 tag=1 hlen=3 plen=524 new-ctb
    :pubkey enc packet: version 3, algo 1, keyid 9D8C454A43A6D2DE
    data: [4094 bits]
    # off=1581 ctb=d2 tag=18 hlen=3 plen=1718 new-ctb
    :encrypted data packet:
    length: 1718
    mdc_method: 2

As before, the reason given for “public key decryption failed” depends
on the card reader used:

  * SCM SPR332 v2: “Missing item in object”

  * Cherry ST-2000: “Invalid value”

  * REINER SCT cyberJack: “Missing item in object”

It seems like the card reader cannot decrypt the session key. *Is that correct?*

I also tried removing all keys except for my encryption key
04FDF78D1679DD94. This does not make a difference, i.e. encryption fails
as above.

/ Felix