Merge pull request #2736 from cedk/ANSI_X.923

Added support for padding ANSI X.923

3 files changed, 150 insertions, 47 deletions

diff --git a/src/_cffi_src/hazmat_src/padding.c b/src/_cffi_src/hazmat_src/padding.c
index 570bad9f..1a0c869d 100644
--- a/src/_cffi_src/hazmat_src/padding.c
+++ b/src/_cffi_src/hazmat_src/padding.c
@@ -37,3 +37,27 @@ uint8_t Cryptography_check_pkcs7_padding(const uint8_t *data,
     /* Now check the low bit to see if it's set */
     return (mismatch & 1) == 0;
 }
+
+uint8_t Cryptography_check_ansix923_padding(const uint8_t *data,
+                                            uint8_t block_len) {
+    uint8_t i;
+    uint8_t pad_size = data[block_len - 1];
+    uint8_t mismatch = 0;
+    /* Skip the first one with the pad size */
+    for (i = 1; i < block_len; i++) {
+        unsigned int mask = Cryptography_constant_time_lt(i, pad_size);
+        uint8_t b = data[block_len - 1 - i];
+        mismatch |= (mask & b);
+    }
+
+    /* Check to make sure the pad_size was within the valid range. */
+    mismatch |= ~Cryptography_constant_time_lt(0, pad_size);
+    mismatch |= Cryptography_constant_time_lt(block_len, pad_size);
+
+    /* Make sure any bits set are copied to the lowest bit */
+    mismatch |= mismatch >> 4;
+    mismatch |= mismatch >> 2;
+    mismatch |= mismatch >> 1;
+    /* Now check the low bit to see if it's set */
+    return (mismatch & 1) == 0;
+}
diff --git a/src/_cffi_src/hazmat_src/padding.h b/src/_cffi_src/hazmat_src/padding.h
index 4d218b1a..fb023c17 100644
--- a/src/_cffi_src/hazmat_src/padding.h
+++ b/src/_cffi_src/hazmat_src/padding.h
@@ -3,3 +3,4 @@
 // repository for complete details.
 
 uint8_t Cryptography_check_pkcs7_padding(const uint8_t *, uint8_t);
+uint8_t Cryptography_check_ansix923_padding(const uint8_t *, uint8_t);
diff --git a/src/cryptography/hazmat/primitives/padding.py b/src/cryptography/hazmat/primitives/padding.py
index f6491eb7..77fb8f83 100644
--- a/src/cryptography/hazmat/primitives/padding.py
+++ b/src/cryptography/hazmat/primitives/padding.py
@@ -28,14 +28,75 @@ class PaddingContext(object):
         """
 
 
-class PKCS7(object):
-    def __init__(self, block_size):
-        if not (0 <= block_size < 256):
-            raise ValueError("block_size must be in range(0, 256).")
+def _byte_padding_check(block_size):
+    if not (0 <= block_size < 256):
+        raise ValueError("block_size must be in range(0, 256).")
+
+    if block_size % 8 != 0:
+        raise ValueError("block_size must be a multiple of 8.")
+
+
+def _byte_padding_update(buffer_, data, block_size):
+    if buffer_ is None:
+        raise AlreadyFinalized("Context was already finalized.")
+
+    if not isinstance(data, bytes):
+        raise TypeError("data must be bytes.")
+
+    buffer_ += data
+
+    finished_blocks = len(buffer_) // (block_size // 8)
+
+    result = buffer_[:finished_blocks * (block_size // 8)]
+    buffer_ = buffer_[finished_blocks * (block_size // 8):]
+
+    return buffer_, result
+
+
+def _byte_padding_pad(buffer_, block_size, paddingfn):
+    if buffer_ is None:
+        raise AlreadyFinalized("Context was already finalized.")
+
+    pad_size = block_size // 8 - len(buffer_)
+    return buffer_ + paddingfn(pad_size)
+
+
+def _byte_unpadding_update(buffer_, data, block_size):
+    if buffer_ is None:
+        raise AlreadyFinalized("Context was already finalized.")
+
+    if not isinstance(data, bytes):
+        raise TypeError("data must be bytes.")
 
-        if block_size % 8 != 0:
-            raise ValueError("block_size must be a multiple of 8.")
+    buffer_ += data
 
+    finished_blocks = max(len(buffer_) // (block_size // 8) - 1, 0)
+
+    result = buffer_[:finished_blocks * (block_size // 8)]
+    buffer_ = buffer_[finished_blocks * (block_size // 8):]
+
+    return buffer_, result
+
+
+def _byte_unpadding_check(buffer_, block_size, checkfn):
+    if buffer_ is None:
+        raise AlreadyFinalized("Context was already finalized.")
+
+    if len(buffer_) != block_size // 8:
+        raise ValueError("Invalid padding bytes.")
+
+    valid = checkfn(buffer_, block_size // 8)
+
+    if not valid:
+        raise ValueError("Invalid padding bytes.")
+
+    pad_size = six.indexbytes(buffer_, -1)
+    return buffer_[:-pad_size]
+
+
+class PKCS7(object):
+    def __init__(self, block_size):
+        _byte_padding_check(block_size)
         self.block_size = block_size
 
     def padder(self):
@@ -53,27 +114,16 @@ class _PKCS7PaddingContext(object):
         self._buffer = b""
 
     def update(self, data):
-        if self._buffer is None:
-            raise AlreadyFinalized("Context was already finalized.")
-
-        if not isinstance(data, bytes):
-            raise TypeError("data must be bytes.")
-
-        self._buffer += data
-
-        finished_blocks = len(self._buffer) // (self.block_size // 8)
-
-        result = self._buffer[:finished_blocks * (self.block_size // 8)]
-        self._buffer = self._buffer[finished_blocks * (self.block_size // 8):]
-
+        self._buffer, result = _byte_padding_update(
+            self._buffer, data, self.block_size)
         return result
 
-    def finalize(self):
-        if self._buffer is None:
-            raise AlreadyFinalized("Context was already finalized.")
+    def _padding(self, size):
+        return six.int2byte(size) * size
 
-        pad_size = self.block_size // 8 - len(self._buffer)
-        result = self._buffer + six.int2byte(pad_size) * pad_size
+    def finalize(self):
+        result = _byte_padding_pad(
+            self._buffer, self.block_size, self._padding)
         self._buffer = None
         return result
 
@@ -86,39 +136,67 @@ class _PKCS7UnpaddingContext(object):
         self._buffer = b""
 
     def update(self, data):
-        if self._buffer is None:
-            raise AlreadyFinalized("Context was already finalized.")
+        self._buffer, result = _byte_unpadding_update(
+            self._buffer, data, self.block_size)
+        return result
+
+    def finalize(self):
+        result = _byte_unpadding_check(
+            self._buffer, self.block_size,
+            lib.Cryptography_check_pkcs7_padding)
+        self._buffer = None
+        return result
 
-        if not isinstance(data, bytes):
-            raise TypeError("data must be bytes.")
 
-        self._buffer += data
+class ANSIX923(object):
+    def __init__(self, block_size):
+        _byte_padding_check(block_size)
+        self.block_size = block_size
+
+    def padder(self):
+        return _ANSIX923PaddingContext(self.block_size)
+
+    def unpadder(self):
+        return _ANSIX923UnpaddingContext(self.block_size)
 
-        finished_blocks = max(
-            len(self._buffer) // (self.block_size // 8) - 1,
-            0
-        )
 
-        result = self._buffer[:finished_blocks * (self.block_size // 8)]
-        self._buffer = self._buffer[finished_blocks * (self.block_size // 8):]
+@utils.register_interface(PaddingContext)
+class _ANSIX923PaddingContext(object):
+    def __init__(self, block_size):
+        self.block_size = block_size
+        # TODO: more copies than necessary, we should use zero-buffer (#193)
+        self._buffer = b""
 
+    def update(self, data):
+        self._buffer, result = _byte_padding_update(
+            self._buffer, data, self.block_size)
         return result
 
+    def _padding(self, size):
+        return six.int2byte(0) * (size - 1) + six.int2byte(size)
+
     def finalize(self):
-        if self._buffer is None:
-            raise AlreadyFinalized("Context was already finalized.")
+        result = _byte_padding_pad(
+            self._buffer, self.block_size, self._padding)
+        self._buffer = None
+        return result
 
-        if len(self._buffer) != self.block_size // 8:
-            raise ValueError("Invalid padding bytes.")
 
-        valid = lib.Cryptography_check_pkcs7_padding(
-            self._buffer, self.block_size // 8
-        )
+@utils.register_interface(PaddingContext)
+class _ANSIX923UnpaddingContext(object):
+    def __init__(self, block_size):
+        self.block_size = block_size
+        # TODO: more copies than necessary, we should use zero-buffer (#193)
+        self._buffer = b""
 
-        if not valid:
-            raise ValueError("Invalid padding bytes.")
+    def update(self, data):
+        self._buffer, result = _byte_unpadding_update(
+            self._buffer, data, self.block_size)
+        return result
 
-        pad_size = six.indexbytes(self._buffer, -1)
-        res = self._buffer[:-pad_size]
+    def finalize(self):
+        result = _byte_unpadding_check(
+            self._buffer, self.block_size,
+            lib.Cryptography_check_ansix923_padding)
         self._buffer = None
-        return res
+        return result