Add crypto sources for future use.add/crypto

 * the goal is to support AES-CBC-HMAC-SHA as AEAD cipher

Signed-off-by: Toni Uhlig <matzeton@googlemail.com>

1 files changed, 56 insertions, 0 deletions

diff --git a/crypto/pkcs7_padding.c b/crypto/pkcs7_padding.c
new file mode 100644
index 0000000..512f6b6
--- /dev/null
+++ b/crypto/pkcs7_padding.c
@@ -0,0 +1,56 @@
+#include "pkcs7_padding.h"
+
+int pkcs7_padding_pad_buffer( uint8_t *buffer,  size_t data_length, size_t buffer_size, uint8_t modulus ){
+  uint8_t pad_byte = modulus - ( data_length % modulus ) ;
+  if( data_length + pad_byte > buffer_size ){
+    return -pad_byte;
+  }
+  int i = 0;
+  while( i <  pad_byte){
+    buffer[data_length+i] = pad_byte;
+    i++;
+  }
+  return pad_byte;
+}
+
+int pkcs7_padding_valid( uint8_t *buffer, size_t data_length, size_t buffer_size, uint8_t modulus ){
+  uint8_t expected_pad_byte = modulus - ( data_length % modulus ) ;
+  if( data_length + expected_pad_byte > buffer_size ){
+    return 0;
+  }
+  int i = 0;
+  while( i < expected_pad_byte ){
+    if( buffer[data_length + i] != expected_pad_byte){
+      return 0;
+    }
+    i++;
+  }
+  return 1;
+}
+
+size_t pkcs7_padding_data_length( uint8_t * buffer, size_t buffer_size, uint8_t modulus ){
+  /* test for valid buffer size */
+  if( buffer_size % modulus != 0 ||
+    buffer_size < modulus ){
+    return 0;
+  }
+  uint8_t padding_value;
+  padding_value = buffer[buffer_size-1];
+  /* test for valid padding value */
+  if( padding_value < 1 || padding_value > modulus ){
+    return 0;
+  }
+  /* buffer must be at least padding_value + 1 in size */
+  if( buffer_size < padding_value + 1 ){
+    return 0;
+  }
+  uint8_t count = 1;
+  buffer_size --;
+  for( ; count  < padding_value ; count++){
+    buffer_size --;
+    if( buffer[buffer_size] != padding_value ){
+      return 0;
+    }
+  }
+  return buffer_size;
+}
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