diff --git a/trezor_agent/gpg/decode.py b/trezor_agent/gpg/decode.py
index e7d2172..b283350 100644
--- a/trezor_agent/gpg/decode.py
+++ b/trezor_agent/gpg/decode.py
@@ -258,29 +258,23 @@ def parse_packets(stream):
         yield p
 
 
-def digest_packets(packets, hashalg):
+def digest_packets(packets, hasher):
     """Compute digest on specified packets, according to '_to_hash' field."""
     data_to_hash = io.BytesIO()
     for p in packets:
         data_to_hash.write(p['_to_hash'])
-    return hashalg(data_to_hash.getvalue()).digest()
-
-
-def _hash_ripemd160(msg):
-    """Wrapper for ripemd160 hash."""
-    h = hashlib.new("ripemd160")
-    h.update(msg)
-    return h
+    hasher.update(data_to_hash.getvalue())
+    return hasher.digest()
 
 
 HASH_ALGORITHMS = {
-    1: hashlib.md5,
-    2: hashlib.sha1,
-    3: _hash_ripemd160,
-    8: hashlib.sha256,
-    9: hashlib.sha384,
-    10: hashlib.sha512,
-    11: hashlib.sha224,
+    1: 'md5',
+    2: 'sha1',
+    3: 'ripemd160',
+    8: 'sha256',
+    9: 'sha384',
+    10: 'sha512',
+    11: 'sha224',
 }
 
 
@@ -291,13 +285,14 @@ def load_public_key(pubkey_bytes, use_custom=False, ecdh=False):
     pubkey, userid, signature = packets[:3]
     packets = packets[3:]
 
-    hashalg = HASH_ALGORITHMS.get(signature['hash_alg'])
-    if hashalg is not None:
-        digest = digest_packets([pubkey, userid, signature], hashalg)
+    hash_alg = HASH_ALGORITHMS.get(signature['hash_alg'])
+    if hash_alg is not None:
+        digest = digest_packets(packets=[pubkey, userid, signature],
+                                hasher=hashlib.new(hash_alg))
         assert signature['hash_prefix'] == digest[:2]
 
     log.debug('loaded public key "%s"', userid['value'])
-    if hashalg is not None and pubkey.get('verifier'):
+    if hash_alg is not None and pubkey.get('verifier'):
         verify_digest(pubkey=pubkey, digest=digest,
                       signature=signature['sig'], label='GPG public key')
     else:
@@ -324,9 +319,9 @@ def load_public_key(pubkey_bytes, use_custom=False, ecdh=False):
 def load_signature(stream, original_data):
     """Load signature from stream, and compute GPG digest for verification."""
     signature, = list(parse_packets(util.Reader(stream)))
-    hashalg = HASH_ALGORITHMS.get(signature['hash_alg'])
-    assert hashalg is not None
-    digest = digest_packets([{'_to_hash': original_data}, signature], hashalg)
+    hash_alg = HASH_ALGORITHMS[signature['hash_alg']]
+    digest = digest_packets([{'_to_hash': original_data}, signature],
+                            hasher=hashlib.new(hash_alg))
     assert signature['hash_prefix'] == digest[:2]
     return signature, digest