diff --git a/src/cmd_decrypt.rs b/src/cmd_decrypt.rs
index c4c2c51..ec4270f 100644
--- a/src/cmd_decrypt.rs
+++ b/src/cmd_decrypt.rs
@@ -4,7 +4,6 @@ use std::io::{Read, Write};
 use std::path::PathBuf;
 use std::str::FromStr;
 
-use aes_gcm_stream::Aes256GcmStreamDecryptor;
 use openpgp_card::crypto_data::Cryptogram;
 use openpgp_card::OpenPgp;
 use rust_util::{debugging, failure, opt_result, simple_error, success, util_term, XResult};
@@ -15,6 +14,7 @@ use yubikey::YubiKey;
 
 use crate::{file, util};
 use crate::card::get_card;
+use crate::crypto::aes_gcm_decrypt;
 use crate::spec::{TinyEncryptEnvelop, TinyEncryptEnvelopType, TinyEncryptMeta};
 use crate::util::{decode_base64, decode_base64_url_no_pad, ENC_AES256_GCM_P256, simple_kdf, TINY_ENC_FILE_EXT};
 use crate::wrap_key::WrapKey;
@@ -104,13 +104,8 @@ fn try_decrypt_key_ecdh(envelop: &TinyEncryptEnvelop, pin: &Option<String>, slot
                 slot_id,
             ), "Decrypt piv failed: {}");
     let key = simple_kdf(decrypted_shared_secret.as_slice());
-    let key: [u8; 32] = opt_result!(key.as_slice().try_into(), "Invalid envelop: {}");
-    let mut aes256_gcm = Aes256GcmStreamDecryptor::new(key, &wrap_key.nonce);
-    let mut b1 = aes256_gcm.update(&wrap_key.encrypted_data);
-    let b2 = opt_result!(aes256_gcm.finalize(), "Invalid envelop: {}");
-    b1.extend_from_slice(&b2);
-
-    Ok(b1)
+    let decrypted_key = aes_gcm_decrypt(&key, &wrap_key.nonce, &wrap_key.encrypted_data)?;
+    Ok(decrypted_key)
 }
 
 fn try_decrypt_key_pgp(envelop: &TinyEncryptEnvelop, pin: &Option<String>) -> XResult<Vec<u8>> {
diff --git a/src/crypto.rs b/src/crypto.rs
index 38b966a..75e5284 100644
--- a/src/crypto.rs
+++ b/src/crypto.rs
@@ -1,3 +1,14 @@
+use aes_gcm_stream::Aes256GcmStreamDecryptor;
+use rust_util::{opt_result, XResult};
+
+pub fn aes_gcm_decrypt(key: &[u8], nonce: &[u8], message: &[u8]) -> XResult<Vec<u8>> {
+    let key: [u8; 32] = opt_result!(key.try_into(), "Invalid envelop: {}");
+    let mut aes256_gcm = Aes256GcmStreamDecryptor::new(key, nonce);
+    let mut b1 = aes256_gcm.update(message);
+    let b2 = opt_result!(aes256_gcm.finalize(), "Invalid envelop: {}");
+    b1.extend_from_slice(&b2);
+    Ok(b1)
+}
 
 #[test]
 fn test_aes_gcm_01() {