Initial QSfera import

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

@@ -0,0 +1,63 @@
+package dsig
+
+import (
+	"crypto"
+	"crypto/rsa"
+	"fmt"
+	"io"
+)
+
+func rsaGetSignerCryptoSignerKey(key any) (crypto.Signer, bool, error) {
+	if !isValidRSAKey(key) {
+		return nil, false, fmt.Errorf(`invalid key type %T for RSA algorithm`, key)
+	}
+	cs, isCryptoSigner := key.(crypto.Signer)
+	if isCryptoSigner {
+		return cs, true, nil
+	}
+	return nil, false, nil
+}
+
+// rsaPSSOptions returns the PSS options for RSA-PSS signatures with the specified hash.
+// The salt length is set to equal the hash length as per RFC 7518.
+func rsaPSSOptions(h crypto.Hash) rsa.PSSOptions {
+	return rsa.PSSOptions{
+		Hash:       h,
+		SaltLength: rsa.PSSSaltLengthEqualsHash,
+	}
+}
+
+// SignRSA generates an RSA signature for the given payload using the specified private key and options.
+// The raw parameter should be the pre-computed signing input (typically header.payload).
+// If pss is true, RSA-PSS is used; otherwise, PKCS#1 v1.5 is used.
+//
+// The rr parameter is an optional io.Reader that can be used to provide randomness for signing.
+// If rr is nil, it defaults to rand.Reader.
+func SignRSA(key *rsa.PrivateKey, payload []byte, h crypto.Hash, pss bool, rr io.Reader) ([]byte, error) {
+	if !isValidRSAKey(key) {
+		return nil, fmt.Errorf(`invalid key type %T for RSA algorithm`, key)
+	}
+	var opts crypto.SignerOpts = h
+	if pss {
+		rsaopts := rsaPSSOptions(h)
+		opts = &rsaopts
+	}
+	return cryptosign(key, payload, h, opts, rr)
+}
+
+// VerifyRSA verifies an RSA signature for the given payload and header.
+// This function constructs the signing input by encoding the header and payload according to JWS specification,
+// then verifies the signature using the specified public key and hash algorithm.
+// If pss is true, RSA-PSS verification is used; otherwise, PKCS#1 v1.5 verification is used.
+func VerifyRSA(key *rsa.PublicKey, payload, signature []byte, h crypto.Hash, pss bool) error {
+	if !isValidRSAKey(key) {
+		return fmt.Errorf(`invalid key type %T for RSA algorithm`, key)
+	}
+	hasher := h.New()
+	hasher.Write(payload)
+	digest := hasher.Sum(nil)
+	if pss {
+		return rsa.VerifyPSS(key, h, digest, signature, &rsa.PSSOptions{Hash: h, SaltLength: rsa.PSSSaltLengthEqualsHash})
+	}
+	return rsa.VerifyPKCS1v15(key, h, digest, signature)
+}