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Make ed25519 keys generated by Packer serialize in the format usable by ssh #120

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merged 1 commit into from Aug 12, 2022
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Make ed25519 keys generated by Packer serialize in the format usable by ssh #120

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25 changes: 21 additions & 4 deletions communicator/sshkey/generate.go
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Expand Up @@ -62,12 +62,14 @@ func NewPair(public, private interface{}) (*Pair, error) {
}, nil
}

// PairFromED25519 marshalls a valid pair of openssh pem for ED25519 keypairs.
// NewPair can handle ed25519 pairs but generates the wrong format apparently:
// `Load key "id_ed25519": invalid format` is the error that happens when I try
// to ssh with such a key.
// PairFromED25519 marshals a valid pair of openssh pem for ED25519 keypairs.
func PairFromED25519(public ed25519.PublicKey, private ed25519.PrivateKey) (*Pair, error) {
// see https://github.com/golang/crypto/blob/7f63de1d35b0f77fa2b9faea3e7deb402a2383c8/ssh/keys.go#L1273-L1443
// and https://github.com/openssh/openssh-portable/blob/master/PROTOCOL.key
// Also the right cipher block size for padding could be found here
// https://github.com/openssh/openssh-portable/blob/eba523f0a130f1cce829e6aecdcefa841f526a1a/cipher.c#L112
const noneCipherBlockSize = 8

key := struct {
Pub []byte
Priv []byte
Expand All @@ -90,6 +92,20 @@ func PairFromED25519(public ed25519.PublicKey, private ed25519.PrivateKey) (*Pai
}
pk1Bytes := ssh.Marshal(pk1)

pubk1 := struct {
Keytype string
Key []byte
}{
Keytype: ssh.KeyAlgoED25519,
Key: public,
}
pubk1Bytes := ssh.Marshal(pubk1)

padLen := noneCipherBlockSize - (len(pk1Bytes) % noneCipherBlockSize)
for i := 1; i <= padLen; i++ {
pk1Bytes = append(pk1Bytes, byte(i))
}

k := struct {
CipherName string
KdfName string
Expand All @@ -102,6 +118,7 @@ func PairFromED25519(public ed25519.PublicKey, private ed25519.PrivateKey) (*Pai
KdfName: "none",
KdfOpts: "",
NumKeys: 1,
PubKey: pubk1Bytes,
PrivKeyBlock: pk1Bytes,
}

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