Cannot export SSH public key

[Felix E. Klee]

Thanks, Ingo!

Looking at my log, I realize that I indeed uploaded the primary key when
I did `keytocard`. I did not do `key 2` to select the authentication sub
key. Instead I was assuming that GnuPG does automatically select the
right sub key. There was a warning about moving the primary key, which I
ignored.

Today I fixed that, and now all works consistently:

    $ gpg --card-status
    […]
    Signature key ....: 7A0F E73D DB74 4F0F 9734  1DA7 1BE3 49D1 1B6E
    D589
          created ....: 2023-06-29 03:50:43
    Encryption key....: DBBD 3239 D0F1 4326 808D  FC8F 7CC0 2D68 D2E3
    1736
          created ....: 2023-06-29 03:50:43
    Authentication key: 9DFF AD98 566A 604F 7290  7C24 32B1 06F6 877C
    C64B
          created ....: 2023-11-22 15:14:14
    General key info..: pub  rsa4096/1BE349D11B6ED589 2023-06-29 Felix
    E. Klee (YubiKey) <yubikey at f76.eu>
    sec>  rsa4096/1BE349D11B6ED589  created: 2023-06-29  expires: never
                                    card-no: 0006 18698015
    ssb>  rsa4096/7CC02D68D2E31736  created: 2023-06-29  expires: never
                                    card-no: 0006 18698015
    ssb>  rsa4096/32B106F6877CC64B  created: 2023-11-22  expires: never
                                    card-no: 0006 18698015
    $ gpg --export-ssh-key yubikey
    ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAACAQC1jJSXxnM4iR3F16Yd5FEjrOo6sbGF
    rkvVVoqUt9iyL5Z+Lz1ElpyUoKcGRRtU8NNueI8RpJT7ipIxubMiefDHVU7FRhk809jQ
    vlTu8YDezdIZ0BWJ3W9+CCCQkD9JNmr5LsUnqD5KKUP4v0rwN6zLsXARGjpv1Jj61vJe
    o3+B9CGpe8cIFvbdVw7QEi5t1hW9ghRrHDREXhIYkc51rzK4htBBdlX7E4yFuiuPZC/2
    Q2lUelBrHP+bwgC+GzliHUIseuGAGEpSjJadtuSC2gUZbgv7PN6jM7WzaSdJ22spoFlP
    XoIimu4hSOpEgK/txOuB+ge3MrpXEQPYW1tN0nD1RZF39uGbGdQrk9s6MARbZ+1APTJh
    H6oi9fPfOp7EEkmZsm1ojwGoIN+RoYQ23KMVqI915SNn5CaRySQNenVyAJ7Skl2Q3bdK
    ENW7lkGFXZ/DxpA8dQITZGBJEGhVppj2Pfp4uANDcdqUUGCN3i0srmkb7XaNn3U9qyIB
    KEgnFupkNfMVB48AQu1PYxoEoO/zIyTVlPn0iSAl64zA27u5RXlikEbx0ePvPSYuMTL4
    ZaDk2vNvKNmPvXBi6dZvXIPx2ROrqBrLMNx19EHDVSSVT+R3Qf1f/4TwRdHPb6ZliSFv
    FF6eygY40y5whHNy7Q8zxrj5Py56Cp+Alus3jr6UNw== openpgp:0x877CC64B
    $ ssh-add -L
    ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAACAQC1jJSXxnM4iR3F16Yd5FEjrOo6sbGF
    rkvVVoqUt9iyL5Z+Lz1ElpyUoKcGRRtU8NNueI8RpJT7ipIxubMiefDHVU7FRhk809jQ
    vlTu8YDezdIZ0BWJ3W9+CCCQkD9JNmr5LsUnqD5KKUP4v0rwN6zLsXARGjpv1Jj61vJe
    o3+B9CGpe8cIFvbdVw7QEi5t1hW9ghRrHDREXhIYkc51rzK4htBBdlX7E4yFuiuPZC/2
    Q2lUelBrHP+bwgC+GzliHUIseuGAGEpSjJadtuSC2gUZbgv7PN6jM7WzaSdJ22spoFlP
    XoIimu4hSOpEgK/txOuB+ge3MrpXEQPYW1tN0nD1RZF39uGbGdQrk9s6MARbZ+1APTJh
    H6oi9fPfOp7EEkmZsm1ojwGoIN+RoYQ23KMVqI915SNn5CaRySQNenVyAJ7Skl2Q3bdK
    ENW7lkGFXZ/DxpA8dQITZGBJEGhVppj2Pfp4uANDcdqUUGCN3i0srmkb7XaNn3U9qyIB
    KEgnFupkNfMVB48AQu1PYxoEoO/zIyTVlPn0iSAl64zA27u5RXlikEbx0ePvPSYuMTL4
    ZaDk2vNvKNmPvXBi6dZvXIPx2ROrqBrLMNx19EHDVSSVT+R3Qf1f/4TwRdHPb6ZliSFv
    FF6eygY40y5whHNy7Q8zxrj5Py56Cp+Alus3jr6UNw== cardno:18 698 015
    ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAACAQC1jJSXxnM4iR3F16Yd5FEjrOo6sbGF
    rkvVVoqUt9iyL5Z+Lz1ElpyUoKcGRRtU8NNueI8RpJT7ipIxubMiefDHVU7FRhk809jQ
    vlTu8YDezdIZ0BWJ3W9+CCCQkD9JNmr5LsUnqD5KKUP4v0rwN6zLsXARGjpv1Jj61vJe
    o3+B9CGpe8cIFvbdVw7QEi5t1hW9ghRrHDREXhIYkc51rzK4htBBdlX7E4yFuiuPZC/2
    Q2lUelBrHP+bwgC+GzliHUIseuGAGEpSjJadtuSC2gUZbgv7PN6jM7WzaSdJ22spoFlP
    XoIimu4hSOpEgK/txOuB+ge3MrpXEQPYW1tN0nD1RZF39uGbGdQrk9s6MARbZ+1APTJh
    H6oi9fPfOp7EEkmZsm1ojwGoIN+RoYQ23KMVqI915SNn5CaRySQNenVyAJ7Skl2Q3bdK
    ENW7lkGFXZ/DxpA8dQITZGBJEGhVppj2Pfp4uANDcdqUUGCN3i0srmkb7XaNn3U9qyIB
    KEgnFupkNfMVB48AQu1PYxoEoO/zIyTVlPn0iSAl64zA27u5RXlikEbx0ePvPSYuMTL4
    ZaDk2vNvKNmPvXBi6dZvXIPx2ROrqBrLMNx19EHDVSSVT+R3Qf1f/4TwRdHPb6ZliSFv
    FF6eygY40y5whHNy7Q8zxrj5Py56Cp+Alus3jr6UNw== (none)

Weird only is that `ssh-add -L` outputs the key twice.

Logging in via SSH with the authentication sub key now works as
expected, all smooth.