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/*
* Arcfour (RC4) implementation for PuTTY.
*
* Coded from Schneier.
*/
#include <assert.h>
#include "ssh.h"
typedef struct {
unsigned char i, j, s[256];
} ArcfourContext;
static void arcfour_block(void *handle, unsigned char *blk, int len)
{
ArcfourContext *ctx = (ArcfourContext *)handle;
unsigned k;
unsigned char tmp, i, j, *s;
s = ctx->s;
i = ctx->i; j = ctx->j;
for (k = 0; (int)k < len; k++) {
i = (i + 1) & 0xff;
j = (j + s[i]) & 0xff;
tmp = s[i]; s[i] = s[j]; s[j] = tmp;
blk[k] ^= s[(s[i]+s[j]) & 0xff];
}
ctx->i = i; ctx->j = j;
}
static void arcfour_setkey(ArcfourContext *ctx, unsigned char const *key,
unsigned keybytes)
{
unsigned char tmp, k[256], *s;
unsigned i, j;
s = ctx->s;
assert(keybytes <= 256);
ctx->i = ctx->j = 0;
for (i = 0; i < 256; i++) {
s[i] = i;
k[i] = key[i % keybytes];
}
j = 0;
for (i = 0; i < 256; i++) {
j = (j + s[i] + k[i]) & 0xff;
tmp = s[i]; s[i] = s[j]; s[j] = tmp;
}
}
/* -- Interface with PuTTY -- */
/*
* We don't implement Arcfour in SSH-1 because it's utterly insecure in
* several ways. See CERT Vulnerability Notes VU#25309, VU#665372,
* and VU#565052.
*
* We don't implement the "arcfour" algorithm in SSH-2 because it doesn't
* stir the cipher state before emitting keystream, and hence is likely
* to leak data about the key.
*/
static void *arcfour_make_context(void)
{
return snew(ArcfourContext);
}
static void arcfour_free_context(void *handle)
{
sfree(handle);
}
static void arcfour_stir(ArcfourContext *ctx)
{
unsigned char *junk = snewn(1536, unsigned char);
memset(junk, 0, 1536);
arcfour_block(ctx, junk, 1536);
memset(junk, 0, 1536);
sfree(junk);
}
static void arcfour128_key(void *handle, unsigned char *key)
{
ArcfourContext *ctx = (ArcfourContext *)handle;
arcfour_setkey(ctx, key, 16);
arcfour_stir(ctx);
}
static void arcfour256_key(void *handle, unsigned char *key)
{
ArcfourContext *ctx = (ArcfourContext *)handle;
arcfour_setkey(ctx, key, 32);
arcfour_stir(ctx);
}
static void arcfour_iv(void *handle, unsigned char *key)
{
}
const struct ssh2_cipher ssh_arcfour128_ssh2 = {
arcfour_make_context, arcfour_free_context, arcfour_iv, arcfour128_key,
arcfour_block, arcfour_block,
"arcfour128",
1, 128, 0, "Arcfour-128"
};
const struct ssh2_cipher ssh_arcfour256_ssh2 = {
arcfour_make_context, arcfour_free_context, arcfour_iv, arcfour256_key,
arcfour_block, arcfour_block,
"arcfour256",
1, 256, 0, "Arcfour-256"
};
static const struct ssh2_cipher *const arcfour_list[] = {
&ssh_arcfour256_ssh2,
&ssh_arcfour128_ssh2,
};
const struct ssh2_ciphers ssh2_arcfour = {
sizeof(arcfour_list) / sizeof(*arcfour_list),
arcfour_list
};
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