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Signature using SHA256 with DSA and a PEM file as private key
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| package service | |
| import ( | |
| "crypto/dsa" | |
| "crypto/rand" | |
| "crypto/sha256" | |
| "encoding/asn1" | |
| "encoding/base64" | |
| "encoding/pem" | |
| "errors" | |
| "log" | |
| "math/big" | |
| "os" | |
| ) | |
| func encodeSHA256WithDSA() (string, error) { | |
| //read pem file from file system | |
| privateKeyData, err := os.ReadFile("./file.pem") | |
| if err != nil { | |
| log.Fatal(err) | |
| } | |
| hash, err := hash("dataToEncode") | |
| if err != nil { | |
| log.Fatal("hash:", err) | |
| } | |
| out, err := sign(hash, privateKeyData) | |
| return base64.StdEncoding.EncodeToString(out), nil | |
| } | |
| func hash(file []byte) ([]byte, error) { | |
| sum := sha256.Sum256(file) | |
| return sum[:], nil | |
| } | |
| func sign(hash []byte, file []byte) ([]byte, error) { | |
| block, _ := pem.Decode(file) | |
| if block == nil { | |
| return nil, errors.New("Failed to parse private key PEM") | |
| } | |
| priv, error := ParseDSAPrivateKey(block.Bytes) | |
| if error != nil { | |
| return nil, error | |
| } | |
| var s dsaSignature | |
| s.R, s.S, error = dsa.Sign(rand.Reader, priv, hash) | |
| if error != nil { | |
| return nil, error | |
| } | |
| return asn1.Marshal(s) | |
| } | |
| func ParseDSAPrivateKey(der []byte) (*dsa.PrivateKey, error) { | |
| var k struct { | |
| Version int | |
| P *big.Int | |
| Q *big.Int | |
| G *big.Int | |
| Pub *big.Int | |
| Priv *big.Int | |
| } | |
| rest, err := asn1.Unmarshal(der, &k) | |
| if err != nil { | |
| return nil, errors.New("failed to parse DSA key: " + err.Error()) | |
| } | |
| if len(rest) > 0 { | |
| return nil, errors.New("garbage after DSA key") | |
| } | |
| return &dsa.PrivateKey{ | |
| PublicKey: dsa.PublicKey{ | |
| Parameters: dsa.Parameters{ | |
| P: k.P, | |
| Q: k.Q, | |
| G: k.G, | |
| }, | |
| Y: k.Pub, | |
| }, | |
| X: k.Priv, | |
| }, nil | |
| } | |
| type dsaPrivateKey struct { | |
| Version int | |
| P, Q, G, Y, X *big.Int | |
| } | |
| type dsaSignature struct { | |
| R, S *big.Int | |
| } |
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