arc4.c File Reference

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

Go to the source code of this file.

Macros
#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. More...
static void	arc4_xor (void *ctxv, const void *srcv, void *dstv, size_t len)
	Perform ARC4 encryption or decryption. More...
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. More...

Variables
struct cipher_algorithm	arc4_algorithm

Macro Definition Documentation

SWAP

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

Definition at line 27 of file arc4.c.

Function Documentation

FILE_LICENCE()

FILE_LICENCE

(

GPL2_OR_LATER

)

arc4_setkey()

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 42 of file arc4.c.

{
        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;
}

References ctx, arc4_ctx::i, arc4_ctx::j, key, S(), and SWAP.

Referenced by arc4_skip().

arc4_xor()

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 78 of file arc4.c.

{
        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;
}

References ctx, arc4_ctx::i, arc4_ctx::j, len, S(), src, and SWAP.

Referenced by arc4_skip().

arc4_skip()

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 109 of file arc4.c.

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

References arc4_setkey(), arc4_xor(), ctx, key, NULL, and src.

Referenced by tkip_kie_decrypt().

Variable Documentation

arc4_algorithm

struct cipher_algorithm arc4_algorithm

Initial value:

= {
        .name = "ARC4",
        .ctxsize = ARC4_CTX_SIZE,
        .blocksize = 1,
        .alignsize = 1,
        .authsize = 0,
        .setkey = arc4_setkey,
        .setiv = cipher_null_setiv,
        .encrypt = arc4_xor,
        .decrypt = arc4_xor,
        .auth = cipher_null_auth,
}

Definition at line 118 of file arc4.c.

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