diff --git a/cmd/tuf/add_signatures.go b/cmd/tuf/add_signatures.go
index 65087360..d825b1b0 100644
--- a/cmd/tuf/add_signatures.go
+++ b/cmd/tuf/add_signatures.go
@@ -1,6 +1,7 @@
 package main
 
 import (
+	"encoding/base64"
 	"encoding/json"
 	"fmt"
 	"os"
@@ -12,25 +13,46 @@ import (
 
 func init() {
 	register("add-signatures", cmdAddSignature, `
-usage: tuf add-signatures --signatures <sig_file> <metadata>
+usage: tuf add-signatures --signatures=<sig_file> [--format=<format>] [--key-id=<key-id>] <metadata>
 
 Adds signatures (the output of "sign-payload") to the given role metadata file.
 
 If the signature does not verify, it will not be added.
+
+Options:
+  --signatures=<sig_file>  the path to the file containing the signature(s)
+  --format=<format>    One of 'json', 'hex', or 'base64'. Defaults to 'json'
+  --key-id=<key-id>    The key-id of the signature being added. Only required if the format is not 'json'
 `)
 }
 
 func cmdAddSignature(args *docopt.Args, repo *tuf.Repo) error {
 	roleFilename := args.String["<metadata>"]
 
-	f := args.String["<sig_file>"]
+	f := args.String["--signatures"]
 	sigBytes, err := os.ReadFile(f)
 	if err != nil {
 		return err
 	}
 	sigs := []data.Signature{}
-	if err = json.Unmarshal(sigBytes, &sigs); err != nil {
-		return err
+	switch args.String["--format"] {
+	case "base64":
+		base64bytes, err := base64.StdEncoding.DecodeString(string(sigBytes))
+		if err != nil {
+			return err
+		}
+		sigs = append(sigs, data.Signature{KeyID: args.String["--key-id"], Signature: base64bytes})
+	case "hex":
+		hex := data.HexBytes{}
+		if err = hex.FromString(sigBytes); err != nil {
+			return err
+		}
+		sigs = append(sigs, data.Signature{KeyID: args.String["--key-id"], Signature: hex})
+	case "json":
+	default:
+		if err = json.Unmarshal(sigBytes, &sigs); err != nil {
+			return err
+		}
 	}
 	for _, sig := range sigs {
 		if err = repo.AddOrUpdateSignature(roleFilename, sig); err != nil {
diff --git a/data/hex_bytes.go b/data/hex_bytes.go
index ec200412..36e5a5a3 100644
--- a/data/hex_bytes.go
+++ b/data/hex_bytes.go
@@ -20,6 +20,15 @@ func (b *HexBytes) UnmarshalJSON(data []byte) error {
 	*b = res
 	return nil
 }
+func (b *HexBytes) FromString(data []byte) error {
+	res := make([]byte, hex.DecodedLen(len(data)))
+	_, err := hex.Decode(res, data)
+	if err != nil {
+		return err
+	}
+	*b = res
+	return nil
+}
 
 func (b HexBytes) MarshalJSON() ([]byte, error) {
 	res := make([]byte, hex.EncodedLen(len(b))+2)