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valentinconan/EncodeSHA256WithDSA.go

Last active June 28, 2023 21:54
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  1. valentinconan revised this gist Jun 28, 2023. No changes.
  2. valentinconan created this gist Jun 28, 2023.
    97 changes: 97 additions & 0 deletions EncodeSHA256WithDSA.go
    View file
    Original file line number Diff line number Diff line change
    @@ -0,0 +1,97 @@
    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
    }