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package sshsig
import (
"errors"
"fmt"
"golang.org/x/crypto/ssh"
)
var (
// ErrUnsupportedSignatureVersion is returned when the signature version is
// not supported.
ErrUnsupportedSignatureVersion = errors.New("unsupported signature version")
// ErrInvalidMagicPreamble is returned when the magic preamble is invalid.
ErrInvalidMagicPreamble = errors.New("invalid magic preamble")
)
// sigVersion is the supported version of the SSH signature format.
// xref: https://github.com/openssh/openssh-portable/blob/V_9_2_P1/PROTOCOL.sshsig#L35
const sigVersion = 1
// magicPreamble is the six-byte sequence "SSHSIG". It is included to
// ensure that manual signatures can never be confused with any message
// signed during SSH user or host authentication.
// xref: https://github.com/openssh/openssh-portable/blob/V_9_2_P1/PROTOCOL.sshsig#L89-L91
var magicPreamble = [6]byte{'S', 'S', 'H', 'S', 'I', 'G'}
// signedData represents data that is signed.
// xref: https://github.com/openssh/openssh-portable/blob/V_9_2_P1/PROTOCOL.sshsig#L79
type signedData struct {
Namespace string
Reserved string
HashAlgorithm string
Hash string
}
// Marshal returns the signed data in SSH wire format.
func (s signedData) Marshal() []byte {
return append(magicPreamble[:], ssh.Marshal(s)...)
}
// blob represents the SSH signature blob.
// xref: https://github.com/openssh/openssh-portable/blob/V_9_2_P1/PROTOCOL.sshsig#L32
type blob struct {
// MagicPreamble is included in the struct to ensure we can unmarshal the
// blob correctly.
MagicPreamble [6]byte
Version uint32
PublicKey string
Namespace string
Reserved string
HashAlgorithm string
Signature string
}
// Validate returns an error if the blob is invalid. This does not check the
// signature itself.
func (b blob) Validate() error {
if b.Version != sigVersion {
return fmt.Errorf("%w %d: expected %d", ErrUnsupportedSignatureVersion, b.Version, sigVersion)
}
if b.MagicPreamble != magicPreamble {
return fmt.Errorf("%w %q: expected %q", ErrInvalidMagicPreamble, b.MagicPreamble, magicPreamble)
}
if err := HashAlgorithm(b.HashAlgorithm).Supported(); err != nil {
return err
}
return nil
}
// Marshal returns the blob in SSH wire format.
func (b blob) Marshal() []byte {
copy(b.MagicPreamble[:], magicPreamble[:])
return ssh.Marshal(b)
}
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