Added kernel MPPE patches (2.2.20 kernel only!) from Frank Cusack.

[ppp.git] / linux / mppe / arcfour.c

diff --git a/linux/mppe/arcfour.c b/linux/mppe/arcfour.c
new file mode 100644 (file)
index 0000000..35b3f42
--- /dev/null
+++ b/linux/mppe/arcfour.c
@@ -0,0 +1,72 @@
+/*
+ * arcfour.c
+ * by Frank Cusack <frank@google.com>
+ * 100% public domain
+ *
+ * Implemented from the description in _Applied Cryptography_, 2nd ed.
+ *
+ * ** Distribution ** of this software is unlimited and unrestricted.
+ *
+ * ** Use ** of this software is almost certainly legal; however, refer
+ * to <http://theory.lcs.mit.edu/~rivest/faq.html>.
+ */
+
+#include "arcfour.h"
+
+#define swap(a, b)             \
+{                              \
+    unsigned char t = b;       \
+    b = a;                     \
+    a = t;                     \
+}
+
+/*
+ * Initialize arcfour from a key.
+ */
+void
+arcfour_setkey(arcfour_context *context, const unsigned char *key,
+              unsigned keylen)
+{
+    unsigned i, j;
+    unsigned char K[256];
+
+    context->i = context->j = 0;
+
+    for (i = 0; i < 256; i++) {
+       context->S[i] = i;
+       K[i] = key[i % keylen];
+    }
+
+    j = 0;
+    for (i = 0; i < 256; i++) {
+       j = (j + context->S[i] + K[i]) % 256;
+       swap(context->S[i], context->S[j]);
+    }
+
+    memset(K, 0, sizeof(K));
+}
+
+/*
+ * plaintext -> ciphertext (or vice versa)
+ */
+void
+arcfour_encrypt(arcfour_context *context, const unsigned char *in, unsigned len,
+               unsigned char *out)
+{
+    unsigned i = context->i;
+    unsigned j = context->j;
+    unsigned char *S = context->S;
+    unsigned char K;
+
+    while (len--) {
+       i = (i + 1) % 256;
+       j = (j + S[i]) % 256;
+       swap(S[i], S[j]);
+       K = S[(S[i] + S[j]) % 256];
+       *out++ = *in++ ^ K;
+    }
+
+    context->i = i;
+    context->j = j;
+}
+