Resurrect src/XOR.c

This partly reverts commit 5b5b496c0f81f3595d0aebb8da5196492abae429.

--author='akuchling <akuchling@rivest.dlitz.net>' used so that "git blame"
will show the true author of the source code.  The author of this *commit* is
Dwayne C. Litzenberger.

1 files changed, 52 insertions, 0 deletions

diff --git a/src/XOR.c b/src/XOR.c
new file mode 100644
index 0000000..f2c74af
--- /dev/null
+++ b/src/XOR.c
@@ -0,0 +1,52 @@
+/*
+ *  xor.c : Source for the trivial cipher which XORs the message with the key.
+ *          The key can be up to 32 bytes long.
+ *
+ * Part of the Python Cryptography Toolkit
+ *
+ * Distribute and use freely; there are no restrictions on further 
+ * dissemination and usage except those imposed by the laws of your 
+ * country of residence.
+ *
+ */
+
+#define MODULE_NAME XOR
+#define BLOCK_SIZE 1
+#define KEY_SIZE 0
+
+typedef struct 
+{
+	unsigned char key[32];
+	int keylen, last_pos;
+} stream_state;
+
+static void
+stream_init(stream_state *self, unsigned char *key, int len)
+{
+	int i;
+  
+	if (32 <= len) len=32;
+	self->keylen = len;
+	self->last_pos = 0;
+
+	for(i=0; i<len; i++)
+	{
+		self->key[i] = key[i];
+	}
+}
+
+/* Encryption and decryption are symmetric */
+#define stream_decrypt stream_encrypt	
+
+static void stream_encrypt(stream_state *self, unsigned char *block, 
+			   int len)
+{
+	int i, j = self->last_pos;
+	for(i=0; i<len; i++, j=(j+1) % self->keylen)
+	{
+		block[i] ^= self->key[j];
+	}
+	self->last_pos = j;
+}
+
+#include "stream_template.c"