Added load_ssh_rsa_public_key to hazmat.primitives.serialization to allow for loading of OpenSSH RSA public keys

Also added load_ssh_public_key as a generic method that can be later extended to support more public key algorithms.

1 files changed, 47 insertions, 0 deletions

diff --git a/src/cryptography/hazmat/primitives/serialization.py b/src/cryptography/hazmat/primitives/serialization.py
index b9cf5967..0f07e41f 100644
--- a/src/cryptography/hazmat/primitives/serialization.py
+++ b/src/cryptography/hazmat/primitives/serialization.py
@@ -4,9 +4,13 @@
 
 from __future__ import absolute_import, division, print_function
 
+import base64
+import struct
 import warnings
 
 from cryptography import utils
+from cryptography.exceptions import UnsupportedAlgorithm
+from cryptography.hazmat.primitives.asymmetric.rsa import RSAPublicNumbers
 
 
 def load_pem_traditional_openssl_private_key(data, password, backend):
@@ -39,3 +43,46 @@ def load_pem_private_key(data, password, backend):
 
 def load_pem_public_key(data, backend):
     return backend.load_pem_public_key(data)
+
+
+def load_ssh_public_key(data, backend):
+    if not data.startswith(b'ssh-'):
+        raise ValueError('SSH-formatted keys must begin with ssh-')
+
+    if not data.startswith(b'ssh-rsa'):
+        raise UnsupportedAlgorithm('Only RSA keys are currently supported.')
+
+    return load_ssh_rsa_public_key(data, backend)
+
+
+def load_ssh_rsa_public_key(data, backend):
+    if not data.startswith(b'ssh-rsa '):
+        raise ValueError('SSH-formatted RSA keys must begin with ssh-rsa')
+
+    parts = data.split(b' ')
+    data = base64.b64decode(parts[1])
+
+    cert_data = []
+
+    while len(data) > 0:
+        str_len = struct.unpack('>I', data[0:4])[0]
+        cert_data.append(data[4:4 + str_len])
+        data = data[4 + str_len:]
+
+    e = _bytes_to_int(cert_data[1])
+    n = _bytes_to_int(cert_data[2])
+    return backend.load_rsa_public_numbers(RSAPublicNumbers(e, n))
+
+
+def _bytes_to_int(data):
+    if len(data) % 4 != 0:
+        # Pad the bytes with 0x00 to a block size of 4
+        data = (b'\x00' * (4 - (len(data) % 4))) + data
+
+    result = 0
+
+    while len(data) > 0:
+        result = (result << 32) + struct.unpack('>I', data[0:4])[0]
+        data = data[4:]
+
+    return result