BLS key script improvement: allow hex string input (flashbots#611)

* bls key script

* https://github.com/dvush/bls-vanity

scripts/create-bls-keypair/main.go

@@ -1,23 +1,50 @@
 package main
 
+// See also https://github.com/dvush/bls-vanity for creating vanity BLS keys!
+
 import (
 	"fmt"
 	"log"
 
+	"github.com/ethereum/go-ethereum/common/hexutil"
 	"github.com/flashbots/go-boost-utils/bls"
 )
 
 func main() {
+	sk := GenSecretKey()
+	// sk := SecretKeyFromHexString("0x")
+
+	// Convert secret key to public key
+	blsPubkey, err := bls.PublicKeyFromSecretKey(sk)
+	if err != nil {
+		log.Fatal(err.Error())
+	}
+
+	// Print secret key and public key
+	fmt.Printf("secret key: 0x%x\n", bls.SecretKeyToBytes(sk))
+	fmt.Printf("public key: 0x%x\n", bls.PublicKeyToBytes(blsPubkey))
+}
+
+// GenSecretKey generates a random secret key
+func GenSecretKey() *bls.SecretKey {
 	sk, _, err := bls.GenerateNewKeypair()
 	if err != nil {
 		log.Fatal(err.Error())
 	}
+	return sk
+}
 
-	blsPubkey, err := bls.PublicKeyFromSecretKey(sk)
+// SecretKeyFromHexString converts a hex string to a BLS secret key
+func SecretKeyFromHexString(secretKeyHex string) *bls.SecretKey {
+	skBytes, err := hexutil.Decode(secretKeyHex)
 	if err != nil {
 		log.Fatal(err.Error())
 	}
 
-	fmt.Printf("secret key: 0x%x\n", bls.SecretKeyToBytes(sk))
-	fmt.Printf("public key: 0x%x\n", bls.PublicKeyToBytes(blsPubkey))
+	blsSecretKey, err := bls.SecretKeyFromBytes(skBytes[:])
+	if err != nil {
+		log.Fatal(err.Error())
+	}
+
+	return blsSecretKey
 }