arc4.c File Reference

#include <gpxe/crypto.h>
#include <gpxe/arc4.h>

Go to the source code of this file.

Defines
#define	SWAP(ary, i, j)   ({ u8 temp = ary[i]; ary[i] = ary[j]; ary[j] = temp; })
Functions
	FILE_LICENCE (GPL2_OR_LATER)
static int	arc4_setkey (void *ctxv, const void *keyv, size_t keylen)
	Set ARC4 key.
static void	arc4_xor (void *ctxv, const void *srcv, void *dstv, size_t len)
	Perform ARC4 encryption or decryption.
static void	arc4_setiv (void *ctx __unused, const void *iv __unused)
void	arc4_skip (const void *key, size_t keylen, size_t skip, const void *src, void *dst, size_t msglen)
	Perform ARC4 encryption or decryption, skipping initial keystream bytes.
Variables
struct cipher_algorithm	arc4_algorithm

---

Define Documentation

#define SWAP	(	ary,
		i,
		j		)	({ u8 temp = ary[i]; ary[i] = ary[j]; ary[j] = temp; })

Definition at line 26 of file arc4.c.

Referenced by arc4_setkey(), and arc4_xor().

---

Function Documentation

FILE_LICENCE

(

GPL2_OR_LATER

)

static int arc4_setkey	(	void *	ctxv,
		const void *	keyv,
		size_t	keylen
	)			[static]

Set ARC4 key.

Parameters:

	ctxv	ARC4 encryption context
	keyv	Key to set
	keylen	Length of key

If an initialisation vector is to be used, it should be prepended to the key; ARC4 does not implement the setiv function because there is no standard length for an initialisation vector in the cipher.

Definition at line 41 of file arc4.c.

References arc4_ctx::i, arc4_ctx::j, S(), arc4_ctx::state, SWAP, and u8.

Referenced by arc4_skip().

{
        struct arc4_ctx *ctx = ctxv;
        const u8 *key = keyv;
        u8 *S = ctx->state;
        int i, j;

        for ( i = 0; i < 256; i++ ) {
                S[i] = i;
        }

        for ( i = j = 0; i < 256; i++ ) {
                j = ( j + S[i] + key[i % keylen] ) & 0xff;
                SWAP ( S, i, j );
        }

        ctx->i = ctx->j = 0;
        return 0;
}

static void arc4_xor	(	void *	ctxv,
		const void *	srcv,
		void *	dstv,
		size_t	len
	)			[static]

Perform ARC4 encryption or decryption.

Parameters:

	ctxv	ARC4 encryption context
	srcv	Data to encrypt or decrypt
	dstv	Location to store encrypted or decrypted data
	len	Length of data to operate on

ARC4 is a stream cipher that works by generating a stream of PRNG data based on the key, and XOR'ing it with the data to be encrypted. Since XOR is symmetric, encryption and decryption in ARC4 are the same operation.

If you pass a NULL source or destination pointer, len keystream bytes will be consumed without encrypting any data.

Definition at line 77 of file arc4.c.

References arc4_ctx::i, arc4_ctx::j, S(), src, arc4_ctx::state, SWAP, and u8.

Referenced by arc4_skip().

{
        struct arc4_ctx *ctx = ctxv;
        const u8 *src = srcv;
        u8 *dst = dstv;
        u8 *S = ctx->state;
        int i = ctx->i, j = ctx->j;

        while ( len-- ) {
                i = ( i + 1 ) & 0xff;
                j = ( j + S[i] ) & 0xff;
                SWAP ( S, i, j );
                if ( srcv && dstv )
                        *dst++ = *src++ ^ S[(S[i] + S[j]) & 0xff];
        }

        ctx->i = i;
        ctx->j = j;
}

static void arc4_setiv	(	void *ctx	__unused,
		const void *iv	__unused
	)			[static]

Definition at line 98 of file arc4.c.

{
        /* ARC4 does not use a fixed-length IV */
}

void arc4_skip	(	const void *	key,
		size_t	keylen,
		size_t	skip,
		const void *	src,
		void *	dst,
		size_t	msglen
	)

Perform ARC4 encryption or decryption, skipping initial keystream bytes.

Parameters:

	key	ARC4 encryption key
	keylen	Key length
	skip	Number of bytes of keystream to skip
	src	Message to encrypt or decrypt
	msglen	Length of message

Return values:

dst

Encrypted or decrypted message

Definition at line 114 of file arc4.c.

References arc4_setkey(), arc4_xor(), and NULL.

Referenced by tkip_kie_decrypt().

{
        struct arc4_ctx ctx;
        arc4_setkey ( &ctx, key, keylen );
        arc4_xor ( &ctx, NULL, NULL, skip );
        arc4_xor ( &ctx, src, dst, msglen );
}

---

Variable Documentation

struct cipher_algorithm arc4_algorithm

Initial value:

 {
        .name = "ARC4",
        .ctxsize = ARC4_CTX_SIZE,
        .blocksize = 1,
        .setkey = arc4_setkey,
        .setiv = arc4_setiv,
        .encrypt = arc4_xor,
        .decrypt = arc4_xor,
}

Definition at line 123 of file arc4.c.

Referenced by tkip_decrypt(), tkip_encrypt(), wep_decrypt(), and wep_encrypt().