new, derived from old avr/crypto + cast5

[avr-crypto-lib.git] / arcfour.c

diff --git a/arcfour.c b/arcfour.c
new file mode 100644 (file)
index 0000000..863b7ac
--- /dev/null
+++ b/arcfour.c
@@ -0,0 +1,43 @@
+/* 
+ * File:               arcfour.c
+ * Author:     Daniel Otte
+ * Date:       07.06.2006
+ * License: GPL
+ * Description: Implementation of the ARCFOUR (RC4 compatible) stream cipher algorithm.
+ * 
+ */
+ 
+#include <stdint.h>
+#include "arcfour.h"
+
+/*
+ * length is length of key in bytes!
+ */
+
+void arcfour_init(arcfour_ctx_t *c, uint8_t *key, uint8_t length){
+       uint8_t t;
+       unsigned x,y=0;
+       for(x=0; x<= 255; ++x)
+               c->s[x]=x;
+       
+       for(x=0; x<= 255; ++x){
+               y += c->s[x] + key[x % length];
+               y &= 0xff;
+               t = c->s[y];
+               c->s[y] = c->s[x];
+               c->s[x] = t;
+       };
+               
+       c->i = c->j = 0;
+}
+
+uint8_t arcfour_gen(arcfour_ctx_t *c){
+       uint8_t t;
+       c->i++;
+       c->j += c->s[c->i];
+       t = c->s[c->j];
+       c->s[c->j] = c->s[c->i];
+       c->s[c->i] = t;
+       return c->s[(c->s[c->j] + c->s[c->i]) & 0xff];
+}
+