new, derived from old avr/crypto + cast5

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

diff --git a/prng.c b/prng.c
new file mode 100644 (file)
index 0000000..640c2ac
--- /dev/null
+++ b/prng.c
@@ -0,0 +1,95 @@
+/**
+ * File:               prng.c
+ * Author:             Daniel Otte
+ * Date:               17.05.2006
+ * License:            GPL
+ * Description:        This file contains an implementaition of a pseudo-random-number generator.
+ * Extension 1:
+ *     rndCore is expanded to 512 bits for more security.
+ **/
+
+
+/*
+ * 
+ *                      ####################################################################################
+ *                      #                                                                                                                                                     #
+ *                                         #             +---------------------------+                                                                                    #
+ *                                         #             |                                           |                                                                                    #
+ *                                         #             V                                           |                                                                                    #
+ *                      #      (concat)                                  |                                                                                        #
+ *  +---------------+   #    o---------o             (xor)+---------+      o---------o       o---------o   #    +--------------+
+ *  | entropy Block | -----> | sha-256 | --(offset)-<     | rndCore | ---> | sha-256 | --+-> | sha-256 | -----> | random Block |
+ *  +---------------+   #    o---------o             (xor)+---------+      o---------o   |   o---------o   #    +--------------+
+ *                                             #                                                     (xor)     (xor)                                    |                                 #
+ *                                             #                                                           ^     ^                                              |                                 #
+ *                                             #                                                            \   /                                               |                                 #
+ *                                             #                                                           (offset)---------------------+                                 #
+ *                                             #                                                                                                                                                      #
+ *                                             ####################################################################################
+ * 
+ */
+
+#include <stdint.h>
+#include <string.h>
+#include "sha256.h"
+
+
+
+
+uint32_t rndCore[16]; /* secret */
+
+/*
+ * idea is: hash the message and add it via xor to rndCore
+ *
+ * length in bits 
+ * 
+ * we simply first "hash" rndCore, then entropy.
+ */
+void addEntropy(unsigned length, void* data){
+       sha256_ctx_t s;
+       static uint8_t offset=0; /* selects if higher or lower half gets updated */
+       sha256_init(&s);
+       sha256_nextBlock(&s, rndCore);
+       while (length>=512){
+               sha256_nextBlock(&s, data);
+               data += 512/8;
+               length -= 512;  
+       }
+       sha256_lastBlock(&s, data, length);
+       uint8_t i;
+       for (i=0; i<8; ++i){
+               rndCore[i+offset] ^= s.h[i];
+       }
+       offset ^= 8; /* hehe */
+}
+ 
+void getRandomBlock(uint32_t *b){
+       sha256_ctx_t s;
+       uint8_t offset=8;
+       
+       sha256_init(&s);
+       sha256_lastBlock(&s, rndCore, 512); /* remeber the byte order! */
+       uint8_t i;
+       for (i=0; i<8; ++i){
+               rndCore[i+offset] ^= s.h[i];
+       }
+       offset ^= 8; /* hehe */
+       memcpy(b, s.h, 32); /* back up first hash in b */
+       sha256_init(&s);
+       sha256_lastBlock(&s, b, 256);
+       memcpy(b, s.h, 32);
+}
+ 
+/* this does some simple buffering */
+uint8_t getRandomByte(void){
+       static uint8_t block[32];
+       static uint8_t i=32;
+       
+       if (i==32){
+               getRandomBlock((void*)block);
+               i=0;
+       }       
+       return block[i++];
+}
+ 
+