gpg: ecdh failed in gcry_cipher_decrypt: Checksum error

[Jan Graichen]

With "throw-keyids" enabled, encrypted files do not contain the recipient key IDs. When decrypting, gpg tries all available secret keys until a valid key is found. When there are multiple ECDH keys present, if the *first* key does not match, and a second is tried, all following tries will report an error. gpg exits with and error code, but the message actually _is_ decrypted and printed:

    root@immortal-colt:~# gpg --decrypt secret.gpg
    gpg: error getting version from 'scdaemon': No SmartCard daemon
    gpg: anonymous recipient; trying secret key 842F5314C2E18EFC ...
    gpg: ecdh failed in gcry_cipher_decrypt: Checksum error
    gpg: anonymous recipient; trying secret key B525EE73BB763C0A ...
    gpg: okay, we are the anonymous recipient.
    gpg: encrypted with ECDH key, ID 0000000000000000
    Hello World

Steps to reproduce:

1. Generate two or more keys:

    root@immortal-colt:~# gpg --default-new-key-algo "ed25519/cert,sign+cv25519/encr" --quick-generate-key '<email address hidden>'
    [..]
    root@immortal-colt:~# gpg --default-new-key-algo "ed25519/cert,sign+cv25519/encr" --quick-generate-key '<email address hidden>'
    [..]

2. Enable throw-keyids:

    root@immortal-colt:~# echo throw-keyids >> ~/.gnupg/gpg.conf

3. Encrypt a secret message:

    root@immortal-colt:~# echo 'Hello World' | gpg --encrypt -r <email address hidden> > secret.gpg

4. Try to decrypt:

    root@immortal-colt:~# gpg --decrypt secret.gpg
    gpg: error getting version from 'scdaemon': No SmartCard daemon
    gpg: anonymous recipient; trying secret key 842F5314C2E18EFC ...
    gpg: ecdh failed in gcry_cipher_decrypt: Checksum error
    gpg: anonymous recipient; trying secret key B525EE73BB763C0A ...
    gpg: okay, we are the anonymous recipient.
    gpg: encrypted with ECDH key, ID 0000000000000000
    Hello World

ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: gpg 2.2.27-3ubuntu2.1
ProcVersionSignature: Ubuntu 6.1.0-1014.14-oem 6.1.29
Uname: Linux 6.1.0-1014-oem x86_64
ApportVersion: 2.20.11-0ubuntu82.5
Architecture: amd64
CasperMD5CheckResult: unknown
Date: Tue Jun 20 20:41:33 2023
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: gnupg2
UpgradeStatus: No upgrade log present (probably fresh install)