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package sasquatch
import (
"crypto/rand"
"crypto/rsa"
"crypto/sha256"
"errors"
"fmt"
"golang.org/x/crypto/ssh"
)
const oaepLabel = "charm.sh/v1/ssh-rsa"
type RSARecipient struct {
sshKey ssh.PublicKey
pubKey *rsa.PublicKey
}
var _ Recipient = &RSARecipient{}
func (*RSARecipient) Type() string { return "ssh-rsa" }
func NewRSARecipient(pk ssh.PublicKey) (*RSARecipient, error) {
if pk.Type() != "ssh-rsa" {
return nil, errors.New("SSH public key is not an RSA key")
}
r := &RSARecipient{
sshKey: pk,
}
if pk, ok := pk.(ssh.CryptoPublicKey); ok {
if pk, ok := pk.CryptoPublicKey().(*rsa.PublicKey); ok {
r.pubKey = pk
} else {
return nil, errors.New("unexpected public key type")
}
} else {
return nil, errors.New("pk does not implement ssh.CryptoPublicKey")
}
return r, nil
}
func (r *RSARecipient) Wrap(fileKey []byte) (*Stanza, error) {
l := &Stanza{
Type: "ssh-rsa",
Args: []string{sshFingerprint(r.sshKey)},
}
wrappedKey, err := rsa.EncryptOAEP(sha256.New(), rand.Reader,
r.pubKey, fileKey, []byte(oaepLabel))
if err != nil {
return nil, err
}
l.Body = wrappedKey
return l, nil
}
type RSAIdentity struct {
k *rsa.PrivateKey
sshKey ssh.PublicKey
}
var _ Identity = &RSAIdentity{}
func (*RSAIdentity) Type() string { return "ssh-rsa" }
func NewRSAIdentity(key *rsa.PrivateKey) (*RSAIdentity, error) {
s, err := ssh.NewSignerFromKey(key)
if err != nil {
return nil, err
}
i := &RSAIdentity{
k: key, sshKey: s.PublicKey(),
}
return i, nil
}
func (i *RSAIdentity) Unwrap(block *Stanza) ([]byte, error) {
if block.Type != "ssh-rsa" {
return nil, ErrIncorrectIdentity
}
if len(block.Args) != 1 {
return nil, errors.New("invalid ssh-rsa recipient block")
}
if block.Args[0] != sshFingerprint(i.sshKey) {
return nil, ErrIncorrectIdentity
}
fileKey, err := rsa.DecryptOAEP(sha256.New(), rand.Reader, i.k,
block.Body, []byte(oaepLabel))
if err != nil {
return nil, fmt.Errorf("failed to decrypt file key: %v", err)
}
return fileKey, nil
}
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