drone-yaml/yaml/signer/signer.go

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2019-01-22 23:44:17 +00:00
package signer
import (
"bytes"
"crypto/hmac"
"crypto/sha256"
"encoding/hex"
"errors"
"github.com/drone/drone-yaml/yaml"
goyaml "gopkg.in/yaml.v2"
)
// ErrInvalidKey is returned when the key is missing or
// is less than 32-bytes.
var ErrInvalidKey = errors.New("signer: key must be 32-bytes")
// Key represents 32-byte signature.
type Key []byte
// KeyString is a helper function that returns a Key
// from a string.
func KeyString(s string) Key {
return []byte(s)
}
// Sign calculates and returns the hmac signature of the
// parsed yaml file.
func Sign(data []byte, key Key) (string, error) {
res, err := yaml.ParseRawBytes(data)
if err != nil {
return "", err
}
hmac, err := sign(res, key)
return hex.EncodeToString(hmac), err
}
// SignUpdate calculates the hmac signature of the parsed
// yaml file and adds a signature resource. If a signature
// resource already exists, it is replaced.
func SignUpdate(data []byte, key Key) ([]byte, error) {
res, err := yaml.ParseRawBytes(data)
if err != nil {
return nil, err
}
hmac, err := sign(res, key)
if err != nil {
return nil, err
}
var buf bytes.Buffer
for _, r := range res {
if r.Kind != yaml.KindSignature {
buf.WriteString("---")
buf.WriteByte('\n')
buf.Write(r.Data)
}
}
buf.WriteString("---")
buf.WriteByte('\n')
buf.WriteString("kind: signature")
buf.WriteByte('\n')
buf.WriteString("hmac: " + hex.EncodeToString(hmac))
buf.WriteByte('\n')
buf.WriteByte('\n')
buf.WriteString("...")
buf.WriteByte('\n')
return buf.Bytes(), nil
}
// Verify returns true if the signature of the parsed
// yaml file can be verified.
func Verify(data []byte, key Key) (bool, error) {
res, err := yaml.ParseRawBytes(data)
if err != nil {
return false, err
}
mac1, err := extract(res)
if err != nil {
return false, nil
}
mac2, err := sign(res, key)
if err != nil {
return false, err
}
return hmac.Equal(mac1, mac2), nil
}
// WriteTo writes the signature to the yaml file. If the
// signature already exists it is removed, and the new
// signature is appended to the end of the document.
func WriteTo(data []byte, hmac string) ([]byte, error) {
res, err := yaml.ParseRawBytes(data)
return upsert(res, hmac), err
}
// helper function extracts the hex-encoded signature
// resource from the parsed resource list.
func extract(res []*yaml.RawResource) ([]byte, error) {
for _, r := range res {
if r.Kind == yaml.KindSignature {
out := new(yaml.Signature)
err := goyaml.Unmarshal(r.Data, out)
if err != nil {
return nil, err
}
return hex.DecodeString(out.Hmac)
}
}
return nil, errors.New("yaml: missing signature")
}
// helper function generates a hex-encoded signature
// based on the parsed resource list.
func sign(resources []*yaml.RawResource, key Key) ([]byte, error) {
if len(key) < 32 {
return nil, ErrInvalidKey
}
h := hmac.New(sha256.New, key)
for _, r := range resources {
if r.Kind != yaml.KindSignature {
h.Write(r.Data)
}
}
return h.Sum(nil), nil
}
// helper function inserts or updates the hmac signature
// into the yaml document, and returns an updated copy.
func upsert(res []*yaml.RawResource, hmac string) []byte {
var buf bytes.Buffer
for _, r := range res {
if r.Kind != yaml.KindSignature {
buf.WriteString("---")
buf.WriteByte('\n')
buf.Write(r.Data)
}
}
buf.WriteString("---")
buf.WriteByte('\n')
buf.WriteString("kind: signature")
buf.WriteByte('\n')
buf.WriteString("hmac: " + hmac)
buf.WriteByte('\n')
buf.WriteByte('\n')
buf.WriteString("...")
buf.WriteByte('\n')
return buf.Bytes()
}