1 files changed, 111 insertions, 0 deletions
diff --git a/src/cryptography/hazmat/backends/openssl/aead.py b/src/cryptography/hazmat/backends/openssl/aead.py
new file mode 100644
index 00000000..5eb2e997
--- /dev/null
+++ b/src/cryptography/hazmat/backends/openssl/aead.py
@@ -0,0 +1,111 @@
+# This file is dual licensed under the terms of the Apache License, Version
+# 2.0, and the BSD License. See the LICENSE file in the root of this repository
+# for complete details.
+
+from __future__ import absolute_import, division, print_function
+
+from cryptography.exceptions import InvalidTag
+
+
+_ENCRYPT = 1
+_DECRYPT = 0
+
+
+def _aead_setup(backend, cipher_name, key, nonce, tag, tag_len, operation):
+    evp_cipher = backend._lib.EVP_get_cipherbyname(cipher_name)
+    backend.openssl_assert(evp_cipher != backend._ffi.NULL)
+    ctx = backend._lib.EVP_CIPHER_CTX_new()
+    ctx = backend._ffi.gc(ctx, backend._lib.EVP_CIPHER_CTX_free)
+    res = backend._lib.EVP_CipherInit_ex(
+        ctx, evp_cipher,
+        backend._ffi.NULL,
+        backend._ffi.NULL,
+        backend._ffi.NULL,
+        int(operation == _ENCRYPT)
+    )
+    backend.openssl_assert(res != 0)
+    res = backend._lib.EVP_CIPHER_CTX_set_key_length(ctx, len(key))
+    backend.openssl_assert(res != 0)
+    res = backend._lib.EVP_CIPHER_CTX_ctrl(
+        ctx, backend._lib.EVP_CTRL_AEAD_SET_IVLEN, len(nonce),
+        backend._ffi.NULL
+    )
+    backend.openssl_assert(res != 0)
+    if operation == _DECRYPT:
+        res = backend._lib.EVP_CIPHER_CTX_ctrl(
+            ctx, backend._lib.EVP_CTRL_AEAD_SET_TAG, len(tag), tag
+        )
+        backend.openssl_assert(res != 0)
+    else:
+        res = backend._lib.EVP_CIPHER_CTX_ctrl(
+            ctx, backend._lib.EVP_CTRL_AEAD_SET_TAG, tag_len, backend._ffi.NULL
+        )
+
+    res = backend._lib.EVP_CipherInit_ex(
+        ctx,
+        backend._ffi.NULL,
+        backend._ffi.NULL,
+        key,
+        nonce,
+        int(operation == _ENCRYPT)
+    )
+    backend.openssl_assert(res != 0)
+    return ctx
+
+
+def _process_aad(backend, ctx, associated_data):
+    outlen = backend._ffi.new("int *")
+    res = backend._lib.EVP_CipherUpdate(
+        ctx, backend._ffi.NULL, outlen, associated_data, len(associated_data)
+    )
+    backend.openssl_assert(res != 0)
+
+
+def _process_data(backend, ctx, data):
+    outlen = backend._ffi.new("int *")
+    buf = backend._ffi.new("unsigned char[]", len(data))
+    res = backend._lib.EVP_CipherUpdate(ctx, buf, outlen, data, len(data))
+    backend.openssl_assert(res != 0)
+    return backend._ffi.buffer(buf, outlen[0])[:]
+
+
+def _encrypt(backend, cipher_name, key, nonce, data, associated_data,
+             tag_length):
+    ctx = _aead_setup(
+        backend, cipher_name, key, nonce, None, tag_length, _ENCRYPT
+    )
+
+    _process_aad(backend, ctx, associated_data)
+    processed_data = _process_data(backend, ctx, data)
+    outlen = backend._ffi.new("int *")
+    res = backend._lib.EVP_CipherFinal_ex(ctx, backend._ffi.NULL, outlen)
+    backend.openssl_assert(res != 0)
+    backend.openssl_assert(outlen[0] == 0)
+    tag_buf = backend._ffi.new("unsigned char[]", tag_length)
+    res = backend._lib.EVP_CIPHER_CTX_ctrl(
+        ctx, backend._lib.EVP_CTRL_AEAD_GET_TAG, tag_length, tag_buf
+    )
+    backend.openssl_assert(res != 0)
+    tag = backend._ffi.buffer(tag_buf)[:]
+
+    return processed_data + tag
+
+
+def _decrypt(backend, cipher_name, key, nonce, data, associated_data,
+             tag_length):
+    if len(data) < tag_length:
+        raise InvalidTag
+    tag = data[-tag_length:]
+    data = data[:-tag_length]
+    ctx = _aead_setup(
+        backend, cipher_name, key, nonce, tag, tag_length, _DECRYPT
+    )
+    _process_aad(backend, ctx, associated_data)
+    processed_data = _process_data(backend, ctx, data)
+    outlen = backend._ffi.new("int *")
+    res = backend._lib.EVP_CipherFinal_ex(ctx, backend._ffi.NULL, outlen)
+    if res == 0:
+        backend._consume_errors()
+        raise InvalidTag
+
+    return processed_data