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forgejo/vendor/github.com/42wim/sshsig/encode.go

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// Modified by 42wim
//
// Copyright 2021 The Sigstore Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package sshsig
import (
"errors"
"fmt"
"github.com/42wim/sshsig/pem"
"golang.org/x/crypto/ssh"
)
const (
pemType = "SSH SIGNATURE"
)
// Armored returns the signature in an armored format.
func Armor(s *ssh.Signature, p ssh.PublicKey, ns string) []byte {
sig := WrappedSig{
Version: 1,
PublicKey: string(p.Marshal()),
Namespace: ns,
HashAlgorithm: defaultHashAlgorithm,
Signature: string(ssh.Marshal(s)),
}
copy(sig.MagicHeader[:], magicHeader)
enc := pem.EncodeToMemory(&pem.Block{
Type: pemType,
Bytes: ssh.Marshal(sig),
})
return enc
}
// Decode parses an armored signature.
func Decode(b []byte) (*Signature, error) {
pemBlock, _ := pem.Decode(b)
if pemBlock == nil {
return nil, errors.New("unable to decode pem file")
}
if pemBlock.Type != pemType {
return nil, fmt.Errorf("wrong pem block type: %s. Expected SSH-SIGNATURE", pemBlock.Type)
}
// Now we unmarshal it into the Signature block
sig := WrappedSig{}
if err := ssh.Unmarshal(pemBlock.Bytes, &sig); err != nil {
return nil, err
}
if sig.Version != 1 {
return nil, fmt.Errorf("unsupported signature version: %d", sig.Version)
}
if string(sig.MagicHeader[:]) != magicHeader {
return nil, fmt.Errorf("invalid magic header: %s", sig.MagicHeader[:])
}
if _, ok := supportedHashAlgorithms[sig.HashAlgorithm]; !ok {
return nil, fmt.Errorf("unsupported hash algorithm: %s", sig.HashAlgorithm)
}
// Now we can unpack the Signature and PublicKey blocks
sshSig := ssh.Signature{}
if err := ssh.Unmarshal([]byte(sig.Signature), &sshSig); err != nil {
return nil, err
}
// TODO: check the format here (should be rsa-sha512)
pk, err := ssh.ParsePublicKey([]byte(sig.PublicKey))
if err != nil {
return nil, err
}
return &Signature{
signature: &sshSig,
pk: pk,
hashAlg: sig.HashAlgorithm,
}, nil
}