diff --git a/httpsig.py b/httpsig.py
index 443cd9a2c..88fe0a895 100644
--- a/httpsig.py
+++ b/httpsig.py
@@ -9,26 +9,26 @@ __status__ = "Production"
 
 # see https://tools.ietf.org/html/draft-cavage-http-signatures-06
 
-try:
-    from Cryptodome.PublicKey import RSA
-    from Cryptodome.Hash import SHA256
-    from Cryptodome.Signature import pkcs1_15
-except ImportError:
-    from Crypto.PublicKey import RSA
-    from Crypto.Hash import SHA256
-    # from Crypto.Signature import PKCS1_v1_5
-    from Crypto.Signature import pkcs1_15
-
+from cryptography.hazmat.backends import default_backend
+from cryptography.hazmat.primitives.serialization import load_pem_private_key
+from cryptography.hazmat.primitives.serialization import load_pem_public_key
+from cryptography.hazmat.primitives.asymmetric import padding
+from cryptography.hazmat.primitives import hashes
 import base64
 from time import gmtime, strftime
 import datetime
 from utils import getFullDomain
 
 
+def _getSHA256(msg: str):
+    digest = hashes.Hash(hashes.SHA256(), backend=default_backend())
+    digest.update(msg)
+    return digest.finalize()
+
+
 def messageContentDigest(messageBodyJsonStr: str) -> str:
     msg = messageBodyJsonStr.encode('utf-8')
-    digestStr = SHA256.new(msg).digest()
-    return base64.b64encode(digestStr).decode('utf-8')
+    return base64.b64encode(_getSHA256(msg)).decode('utf-8')
 
 
 def signPostHeaders(dateStr: str, privateKeyPem: str,
@@ -66,7 +66,8 @@ def signPostHeaders(dateStr: str, privateKeyPem: str,
             'content-type': 'application/activity+json',
             'content-length': str(contentLength)
         }
-    privateKeyPem = RSA.import_key(privateKeyPem)
+    key = load_pem_private_key(privateKeyPem.encode('utf-8'),
+                               None, backend=default_backend())
     # headers.update({
     #     '(request-target)': f'post {path}',
     # })
@@ -76,10 +77,11 @@ def signPostHeaders(dateStr: str, privateKeyPem: str,
     for headerKey in signedHeaderKeys:
         signedHeaderText += f'{headerKey}: {headers[headerKey]}\n'
     signedHeaderText = signedHeaderText.strip()
-    headerDigest = SHA256.new(signedHeaderText.encode('ascii'))
+    headerDigest = _getSHA256(signedHeaderText.encode('ascii'))
 
     # Sign the digest
-    rawSignature = pkcs1_15.new(privateKeyPem).sign(headerDigest)
+    rawSignature = key.sign(headerDigest,
+                            padding.PKCS1v15(), hashes.SHA256())
     signature = base64.b64encode(rawSignature).decode('ascii')
 
     # Put it into a valid HTTP signature format
@@ -176,7 +178,8 @@ def verifyPostHeaders(httpPrefix: str, publicKeyPem: str, headers: dict,
     if debug:
         print('DEBUG: verifyPostHeaders ' + method)
 
-    publicKeyPem = RSA.import_key(publicKeyPem)
+    pubkey = load_pem_public_key(publicKeyPem.encode('utf-8'),
+                                 backend=default_backend())
     # Build a dictionary of the signature values
     signatureHeader = headers['signature']
     signatureDict = {
@@ -244,16 +247,19 @@ def verifyPostHeaders(httpPrefix: str, publicKeyPem: str, headers: dict,
         print('DEBUG: signedHeaderList: ' + str(signedHeaderList))
     # Now we have our header data digest
     signedHeaderText = '\n'.join(signedHeaderList)
-    headerDigest = SHA256.new(signedHeaderText.encode('ascii'))
+    headerDigest = _getSHA256(signedHeaderText.encode('ascii'))
 
     # Get the signature, verify with public key, return result
     signature = base64.b64decode(signatureDict['signature'])
 
     try:
-        pubKey = pkcs1_15.new(publicKeyPem)
-        pubKey.verify(headerDigest, signature)
+        pubkey.verify(
+            signature,
+            headerDigest,
+            padding.PKCS1v15(),
+            hashes.SHA256())
         return True
-    except (ValueError, TypeError):
+    except BaseException:
         if debug:
             print('DEBUG: verifyPostHeaders pkcs1_15 verify failure')
         return False