Add vendor (steam)

vendor/github.com/Philipp15b/go-steam/cryptoutil/rsa.go

@@ -0,0 +1,31 @@
+package cryptoutil
+
+import (
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/sha1"
+	"crypto/x509"
+	"errors"
+)
+
+// Parses a DER encoded RSA public key
+func ParseASN1RSAPublicKey(derBytes []byte) (*rsa.PublicKey, error) {
+	key, err := x509.ParsePKIXPublicKey(derBytes)
+	if err != nil {
+		return nil, err
+	}
+	pubKey, ok := key.(*rsa.PublicKey)
+	if !ok {
+		return nil, errors.New("not an RSA public key")
+	}
+	return pubKey, nil
+}
+
+// Encrypts a message with the given public key using RSA-OAEP and the sha1 hash function.
+func RSAEncrypt(pub *rsa.PublicKey, msg []byte) []byte {
+	b, err := rsa.EncryptOAEP(sha1.New(), rand.Reader, pub, msg, nil)
+	if err != nil {
+		panic(err)
+	}
+	return b
+}