cmd/cosign: set default ko.SigningAlgorithm

Signed-off-by: Riccardo Schirone <[email protected]>

Author: ret2libc

cmd/cosign/cli/sign/sign_blob.go

@@ -40,6 +40,7 @@ import (
 	cbundle "github.com/sigstore/cosign/v2/pkg/cosign/bundle"
 	protobundle "github.com/sigstore/protobuf-specs/gen/pb-go/bundle/v1"
 	protocommon "github.com/sigstore/protobuf-specs/gen/pb-go/common/v1"
+	v1 "github.com/sigstore/protobuf-specs/gen/pb-go/common/v1"
 	"github.com/sigstore/rekor/pkg/generated/models"
 	"github.com/sigstore/sigstore-go/pkg/sign"
 	"github.com/sigstore/sigstore/pkg/cryptoutils"
@@ -66,6 +67,13 @@ func SignBlobCmd(ro *options.RootOptions, ko options.KeyOpts, payloadPath string
 	ctx, cancel := context.WithTimeout(context.Background(), ro.Timeout)
 	defer cancel()
 
+	if ko.SigningAlgorithm == "" {
+		ko.SigningAlgorithm, err = signature.FormatSignatureAlgorithmFlag(v1.PublicKeyDetails_PKIX_ECDSA_P256_SHA_256)
+		if err != nil {
+			return nil, fmt.Errorf("formatting signature algorithm: %w", err)
+		}
+	}
+
 	shouldUpload, err := ShouldUploadToTlog(ctx, ko, nil, tlogUpload)
 	if err != nil {
 		return nil, fmt.Errorf("upload to tlog: %w", err)