boxes: a number of improvements

* Algorithm interfaces are no longer required to load partial blocks,
the space for which is allocated dynamically.
* Padding schemes are now also separated, perhaps in the future to
become a "box" parameter.
Consequently, algorithm interfaces are no longer required to implement
padding either.

1 files changed, 87 insertions, 0 deletions

diff --git a/src/padding.c b/src/padding.c
new file mode 100644
index 0000000..08cafb1
--- /dev/null
+++ b/src/padding.c
@@ -0,0 +1,87 @@
+/**
+ * \file
+ * \author Egor Tensin <Egor.Tensin@gmail.com>
+ * \date 2015
+ * \copyright This file is licensed under the terms of the MIT License.
+ *            See LICENSE.txt for details.
+ */
+
+#include <aesni/all.h>
+
+#include <stdlib.h>
+#include <string.h>
+
+static AesNI_StatusCode aesni_extract_padding_size_pkcs7(
+    const void* src,
+    size_t src_size,
+    size_t* padding_size,
+    AesNI_ErrorDetails* err_details)
+{
+    const unsigned char* cursor = (const unsigned char*) src + src_size - 1;
+    *padding_size = *cursor;
+
+    for (size_t i = 1; i < *padding_size; ++i)
+        if (cursor[0 - i] != *padding_size)
+            return aesni_error_invalid_pkcs7_padding(err_details);
+
+    return AESNI_SUCCESS;
+}
+
+AesNI_StatusCode aesni_extract_padding_size(
+    AesNI_PaddingMethod method,
+    const void* src,
+    size_t src_size,
+    size_t* padding_size,
+    AesNI_ErrorDetails* err_details)
+{
+    assert(src);
+    assert(padding_size);
+
+    if (src == NULL)
+        return aesni_error_null_argument(err_details, "src");
+    if (padding_size == NULL)
+        return aesni_error_null_argument(err_details, "padding_size");
+
+    switch (method)
+    {
+        case AESNI_PADDING_PKCS7:
+            return aesni_extract_padding_size_pkcs7(
+                src, src_size, padding_size, err_details);
+
+        default:
+            return aesni_error_not_implemented(
+                err_details, "unsupported padding method");
+    }
+}
+
+static AesNI_StatusCode aesni_fill_with_padding_pkcs7(
+    void* dest,
+    size_t padding_size,
+    AesNI_ErrorDetails* err_details)
+{
+    memset(dest, padding_size, padding_size);
+    return AESNI_SUCCESS;
+}
+
+AesNI_StatusCode aesni_fill_with_padding(
+    AesNI_PaddingMethod method,
+    void* dest,
+    size_t padding_size,
+    AesNI_ErrorDetails* err_details)
+{
+    assert(dest);
+
+    if (dest == NULL)
+        return aesni_error_null_argument(err_details, "dest");
+
+    switch (method)
+    {
+        case AESNI_PADDING_PKCS7:
+            return aesni_fill_with_padding_pkcs7(
+                dest, padding_size, err_details);
+
+        default:
+            return aesni_error_not_implemented(
+                err_details, "unsupported padding method");
+    }
+}