Initial QSfera import

Server/vendor/github.com/lestrrat-go/dsig/crypto_signer.go

@@ -0,0 +1,45 @@
+package dsig
+
+import (
+	"crypto"
+	"crypto/rand"
+	"fmt"
+	"io"
+)
+
+// cryptosign is a low-level function that signs a payload using a crypto.Signer.
+// If hash is crypto.Hash(0), the payload is signed directly without hashing.
+// Otherwise, the payload is hashed using the specified hash function before signing.
+//
+// rr is an io.Reader that provides randomness for signing. If rr is nil, it defaults to rand.Reader.
+func cryptosign(signer crypto.Signer, payload []byte, hash crypto.Hash, opts crypto.SignerOpts, rr io.Reader) ([]byte, error) {
+	if rr == nil {
+		rr = rand.Reader
+	}
+
+	var digest []byte
+	if hash == crypto.Hash(0) {
+		digest = payload
+	} else {
+		h := hash.New()
+		if _, err := h.Write(payload); err != nil {
+			return nil, fmt.Errorf(`failed to write payload to hash: %w`, err)
+		}
+		digest = h.Sum(nil)
+	}
+	return signer.Sign(rr, digest, opts)
+}
+
+// SignCryptoSigner generates a signature using a crypto.Signer interface.
+// This function can be used for hardware security modules, smart cards,
+// and other implementations of the crypto.Signer interface.
+//
+// rr is an io.Reader that provides randomness for signing. If rr is nil, it defaults to rand.Reader.
+//
+// Returns the signature bytes or an error if signing fails.
+func SignCryptoSigner(signer crypto.Signer, raw []byte, h crypto.Hash, opts crypto.SignerOpts, rr io.Reader) ([]byte, error) {
+	if signer == nil {
+		return nil, fmt.Errorf("dsig.SignCryptoSigner: signer is nil")
+	}
+	return cryptosign(signer, raw, h, opts, rr)
+}