gpgsm --gen-key with existing key from "ssh-add" fails

[Daniel Kahn Gillmor]

This was originally reported over on https://dev.gnupg.org/T4892, but it
was requested to move it to the mailing list, so i'm repeating it here.

This was reported by a user on the #gnupg IRC channel on freenode.

With a fresh GNUPGHOME, and gpg-agent acting as ssh-agent:

    ssh-keygen -f ssh-key -N ''
    ssh-add ssh-key
    gpgsm --gen-key

then choose "existing key" and select the keygrip found in sshcontrol. The result is:

    Create self-signed certificate? (y/N) y
    These parameters are used:
        Key-Type: RSA
        Key-Length: 1024
        Key-Grip: 0B4329C87AD80CDCCA1D04C9F0B4FE11378A6F74
        Key-Usage: sign, encrypt
        Serial: random
        Name-DN: CN=Alice
        Name-Email: alice at example.biz

    Proceed with creation? (y/N) y
    Now creating self-signed certificate.  This may take a while ...
    gpgsm: error setting the public key: Invalid S-expression
    gpgsm: error creating certificate request: Invalid S-expression <KSBA>

note that the key created by ssh-key is 3072-bit RSA, not 1024.

Using nettle-bin's sexp-conv, i see:

    2 dkg at alice:/tmp/cdtemp.6ckvQX$ sexp-conv < private-keys-v1.d/A61AD73FB26752B4DAB90F007E6F76467659A19B.key 
    (protected-private-key (rsa (n |AL3C+/cNPCsJ+xKZXOG/u+f1eGM/VsMA7Gs7y1w/
                                    ki3y7fXeVCgV8KXaVQq/4ylfR04aXj3gsrmSDHYX
                                    KYBo69OoGx8tLhhi20ugMAc1qlRuMgmQZDjYGc8U
                                    m4ftOpwKoyKolfPV+PayoXQF0G7aeTC9+kmXxLfv
                                    ZD5DL8UWx/nFTly+5LctlQGshN1+1AZ6U9f4qdRi
                                    by2RpiMa7gdVD1M41RVm+Q2KoMYCs4WMeFgV4+Kj
                                    vxU32O8lLMQ+RpB6Z7Ra/756FeXyATrY7Q2hTGAd
                                    9V9X+vxupsX5MROlg1OfsSRClHVpK1kjiauM+0Zl
                                    oxXEBorRn+qZ51SrimXBaYlAri0zBw0HWg/cc1Xx
                                    pbxWqPrWh5rRrC+wukDG1XiM5LZdWBrZJiT0nYxZ
                                    hzczd9jgjj45XpvcrgK6uiXUWpYPpyjCRAVP/sW1
                                    ZVcm4x8RyYjuvwjh/vKg4F7kludEctnyavQI0utY
                                    62nwESLUuQhKgNvN23Th20iVXGMWOik1GQ==|)
                                (e |AQAB|)
                                (protected openpgp-s2k3-sha1-aes-cbc
                                           ((sha1 |aFmt6IeekIM=|
                                                  "72943616") |cT9DP9U3fOSXE
                                                               elRUvQW1Q==|)
                                           |2BrkPE2deaC3tf+d5rwG2x8QGdilAh+Z
                                            WOoHa/KVlZhvBBIFCfA8g12DamARZTZd
                                            MYIKcjIMDNTlj3I/xJZayzWcm5XliA0O
                                            WqvZJnedJWvjanHLWIu4z5ik+T85fL7E
                                            24/4nrQhTaTFtYo27cgdFgvGxeXbZx9f
                                            VCAhF/Kf12NHDkVEI3qMRBFNd0ofGeTq
                                            4xMtnGd0OfbSG2V51iK0GaexmW4ySkyt
                                            LYpyfMK4Tx/AdwZQAUacJqSs1/ZkoB+R
                                            hTAhW/EsWjHCYeuESZYizUZSuTX9vsGq
                                            If/bVZctTkGQ8jG0qjSpDY9qc8Kjf1wH
                                            ejN1L3qAvXwhDk1bSY+M5XuZ3WgYJgM5
                                            1XL02xQnJl4Eq60lfO9wkRqZEe56PcF+
                                            N4jpNwHcNAHHp58aROm9hsl7u3txAAu2
                                            4d59iGbzkZZFC+3EkC8AxHvhpMCN2vnL
                                            BH/3+THthzcJp4MA8GI5sGsjunHDesT4
                                            LYifUnk99+5bFeCtnnPCNc9kTUDWR0lY
                                            uGYJlmT7frIN+B2EYfaLvlVDlEkoUkM3
                                            aNP8OyViQpQEoLqpTI73/pDMMqOgJWPv
                                            9OgdPk21Ns0/MrKbHxnvKV1Kt7YOZiRI
                                            e7eHjs5PKp2Dk2KxDggwh4B+49o1N+4q
                                            ne/pizT8xNv0kfHaqFj6kfGSA2xevBUK
                                            tLUFvrtenTLV/WtuiLiB56xdG2rDPrmO
                                            VPyzw9B1j2AV2DEfQI6co88rUHO8pLVK
                                            FFqy5nMFnekUrqLITwmSZFPYW24Cf9os
                                            mpeZS/NXfbWITXY+A57mD4l5HGxq3+fu
                                            E5yYNaYoBYkWHTiYDZjdDU5XzU+XoO9A
                                            nFPYrP505dI5aN9QkOdH8HUFp7Qc+6za
                                            j/2MwrULF1BwzT8Lk+Zi6tKE1/K7jH1G
                                            kF5mDjvIfdJktcZU6pLzfIhLHG/egvzy
                                            dzliIDdS72mvsv9l5bWwxqhRNehXn43D
                                            lbSo8mGl1J70EXlXOlXaXnbW8tthlV9c
                                            IXUR1LLHsY5tXuw2UU+aAzlHDxWWlO58
                                            3UPhPUR+ESZCJ3c7uG1MPsIcphAOUVp1
                                            AuqIwYEA77mBvHMjHO1nW+7AS+vyNMOK
                                            iYCnHFZbvDCWHW+8VotsHwSc/8amILBy
                                            AESAbZllfu6nNYNOf4ai2BScUZPu3jNx
                                            /AhWiEK5Vqgv6xWrEi6Xx7/eTR0HhzXE
                                            U0/s5yfl7Rh9ax+2xWz00VEo5l2xHASX
                                            WDGTuhjREufMCgVwccxlMWMVLHiabYi8
                                            rKCtWDJp6c/DgSbGNz6Jy1IL40LPqjaJ
                                            viMmbQKnhmycMyCm+rVcKacVL1a9bYnZ
                                            yqrOplQm4DThEGPSVXn36W+8uSfgosJI
                                            ENvoCme0XnpozjnK5fBI3l1mLFcSvBtp
                                            7RG57f5s/MPNb+5MvrgPSM5xEoeXgyfC|)
                                (protected-at "20200326T010201"))
                           (comment "test at host"))


Any suggestions on what is going wrong here?

    --dkg

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