添加 github.com/pion/dtls 代码

dtls-2.0.9/pkg/crypto/fingerprint/fingerprint.go

@@ -0,0 +1,50 @@
+// Package fingerprint provides a helper to create fingerprint string from certificate
+package fingerprint
+
+import (
+	"crypto"
+	"crypto/x509"
+	"errors"
+	"fmt"
+)
+
+var (
+	errHashUnavailable          = errors.New("fingerprint: hash algorithm is not linked into the binary")
+	errInvalidFingerprintLength = errors.New("fingerprint: invalid fingerprint length")
+)
+
+// Fingerprint creates a fingerprint for a certificate using the specified hash algorithm
+func Fingerprint(cert *x509.Certificate, algo crypto.Hash) (string, error) {
+	if !algo.Available() {
+		return "", errHashUnavailable
+	}
+	h := algo.New()
+	for i := 0; i < len(cert.Raw); {
+		n, _ := h.Write(cert.Raw[i:])
+		// Hash.Writer is specified to be never returning an error.
+		// https://golang.org/pkg/hash/#Hash
+		i += n
+	}
+	digest := []byte(fmt.Sprintf("%x", h.Sum(nil)))
+
+	digestlen := len(digest)
+	if digestlen == 0 {
+		return "", nil
+	}
+	if digestlen%2 != 0 {
+		return "", errInvalidFingerprintLength
+	}
+	res := make([]byte, digestlen>>1+digestlen-1)
+
+	pos := 0
+	for i, c := range digest {
+		res[pos] = c
+		pos++
+		if (i)%2 != 0 && i < digestlen-1 {
+			res[pos] = byte(':')
+			pos++
+		}
+	}
+
+	return string(res), nil
+}