[GH-ISSUE #810] Emails encrypted with Public-Key Encrypted Session Key Packet version 6, unusable with Thunderbird #556

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opened 2026-03-01 17:48:08 +03:00 by kerem · 3 comments

kerem commented

2026-03-01 17:48:08 +03:00

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Originally created by @codematle on GitHub (Feb 8, 2026).
Original GitHub issue: https://github.com/anonaddy/anonaddy/issues/810

Hi,
It seems that when I add a public PGP key the forwarded emails are encrypted (correctly) but with using RFC 9580 somehow.
This prevents Thunderbird from decrypting the message, log:

:armored input
:off 0: packet header 0xc16c (tag 1, len 108)
:off 110: packet header 0xc16c (tag 1, len 108)
:off 220: packet header 0xc16c (tag 1, len 108)
:off 330: packet header 0xd2c896 (tag 18, len 2390)
Symmetrically-encrypted integrity protected data packet

Interestingly, gpg cli also doesn't want to decrypt the message (grabbed from the raw email):

gpg --decrypt
(...)
gpg: packet(1) with unknown version 6

Only sequoia was able to decrypt it (it shows that the message was correctly encrypted for the three decryption subkeys I have):

sq packet dump
(...)
Public-Key Encrypted Session Key Packet, new CTB, 108 bytes
    Version: 6
    Recipient: REDACTED
    Pk algo: ECDH

Public-Key Encrypted Session Key Packet, new CTB, 108 bytes
    Version: 6
    Recipient: REDACTED
    Pk algo: ECDH

Public-Key Encrypted Session Key Packet, new CTB, 108 bytes
    Version: 6
    Recipient: REDACTED
    Pk algo: ECDH
(...)

I've scanned the anonaddy code and it seems to me that it's using gpg to encrypt the messages, which is strange as it's not supposed to support RFC 9580 and packets version 6.

Is this an expected behavior? I have other recipients on addy.io that are encrypted according to RFC 4880, which is compatible with both Thunderbird and GPG:

sq packet dump
(...)
Public-Key Encrypted Session Key Packet, new CTB, 94 bytes
    Version: 3
    Recipient: REDACTED
    Pk algo: ECDH
(...)

Originally created by @codematle on GitHub (Feb 8, 2026). Original GitHub issue: https://github.com/anonaddy/anonaddy/issues/810 Hi, It seems that when I add a public PGP key the forwarded emails are encrypted (correctly) but with using RFC 9580 somehow. This prevents Thunderbird from decrypting the message, log: ``` :armored input :off 0: packet header 0xc16c (tag 1, len 108) :off 110: packet header 0xc16c (tag 1, len 108) :off 220: packet header 0xc16c (tag 1, len 108) :off 330: packet header 0xd2c896 (tag 18, len 2390) Symmetrically-encrypted integrity protected data packet ``` Interestingly, `gpg` cli also doesn't want to decrypt the message (grabbed from the raw email): ``` gpg --decrypt (...) gpg: packet(1) with unknown version 6 ``` Only sequoia was able to decrypt it (it shows that the message was correctly encrypted for the three decryption subkeys I have): ``` sq packet dump (...) Public-Key Encrypted Session Key Packet, new CTB, 108 bytes Version: 6 Recipient: REDACTED Pk algo: ECDH Public-Key Encrypted Session Key Packet, new CTB, 108 bytes Version: 6 Recipient: REDACTED Pk algo: ECDH Public-Key Encrypted Session Key Packet, new CTB, 108 bytes Version: 6 Recipient: REDACTED Pk algo: ECDH (...) ``` I've scanned the anonaddy code and it seems to me that it's using `gpg` to encrypt the messages, which is strange as it's not supposed to support RFC 9580 and packets version 6. Is this an expected behavior? I have other recipients on addy.io that are encrypted according to RFC 4880, which is compatible with both Thunderbird and GPG: ``` sq packet dump (...) Public-Key Encrypted Session Key Packet, new CTB, 94 bytes Version: 3 Recipient: REDACTED Pk algo: ECDH (...) ```

kerem closed this issue

2026-03-01 17:48:08 +03:00

kerem commented

2026-03-01 17:48:09 +03:00

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@willbrowningme commented on GitHub (Feb 10, 2026):

Hmm, all of my encrypted emails are showing version 3.

Are you able to send me an email with the -----BEGIN PGP MESSAGE----- PGP encrypted message and details of the recipient that is happening for?

@willbrowningme commented on GitHub (Feb 10, 2026): Hmm, all of my encrypted emails are showing version 3. Are you able to [send me an email](https://addy.io/contact/) with the `-----BEGIN PGP MESSAGE-----` PGP encrypted message and details of the recipient that is happening for?

kerem commented

2026-03-01 17:48:09 +03:00

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@codematle commented on GitHub (Feb 10, 2026):

Thanks, I just sent you an email with all data titled "PGP version 6 encryption issue".

@codematle commented on GitHub (Feb 10, 2026): Thanks, I just sent you an email with all data titled "PGP version 6 encryption issue".

kerem commented

2026-03-01 17:48:09 +03:00

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Owner

@codematle commented on GitHub (Feb 11, 2026):

Ok, it turns out the key created by Sequoia had SEIPDv2 (“Symmetrically Encrypted Integrity Protected Data” version 2) feature in the Signature Packet. This advertises usage of v6 Public-Key Encrypted Session Key packets to the users according to RFC 9580.
I was able to regenerate the key using gpg - the key now has only SEIPDv1 feature and results in v3 packets when encoded by addy.

@codematle commented on GitHub (Feb 11, 2026): Ok, it turns out the key created by Sequoia had `SEIPDv2` (“Symmetrically Encrypted Integrity Protected Data” version 2) feature in the Signature Packet. This advertises usage of v6 Public-Key Encrypted Session Key packets to the users according to RFC 9580. I was able to regenerate the key using `gpg` - the key now has only `SEIPDv1` feature and results in v3 packets when encoded by addy.

kerem referenced this issue

2026-03-01 17:48:22 +03:00

[PR #556] [CLOSED] rebase #607

kerem referenced this issue

2026-03-14 11:50:42 +03:00

[PR #556] [CLOSED] rebase #1170