123 lines
2.0 KiB
ArmAsm
123 lines
2.0 KiB
ArmAsm
/*
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* File: arcfour-asm.S
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* Author: Daniel Otte
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* Date: 07.06.2006
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* License: GPL
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* Description: Implementation of the ARCFOUR (RC4 compatible) stream cipher algorithm.
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*
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*/
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/* +---+---+---------------------+
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* | i | j | ......<256>........ |
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* +---+---+---------------------+
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*/
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.global arcfour_init
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;== arcfour_init ==
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; this function initialises the context
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; param1: 16-bit pointer to a ctx struct
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; given in r25,r24
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; param2: 16-bit pointer to a key
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; given in r23,r22
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; param1: 8-bit integer indicating keylength in byte
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; given in r20
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arcfour_init:
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push r29
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push r28
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push r2
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movw r26, r24 /* X points to ctx */
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movw r30, r22 /* Z points to key */
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st X+, r1
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st X+, r1 /* X points to S */
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1:
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st X+, r1
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inc r1
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brne 1b
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adiw r24, 2 /* r24:r25 points to S */
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clr r21 /* r21 is j */
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mov r18, r20 /* r18 is keyindex counter */
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clr r0
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2:
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movw r26, r24
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ld r19, Z+
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add r21, r19 /* j+= key[i%length] */
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add r26, r1
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adc r27, r0
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ld r19, X
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add r21, r19 /* j += S[i] */
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dec r18 /* check the key-index counter */
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brne 3f
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movw r30, r22
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mov r18, r20
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3: /* now swap(S[i], S[j]) */ /* r19 is still S[i] */
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movw r28, r24
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add r28, r21
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adc r29, r0 /* Y points to S[j]*/
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ld r2, Y
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st Y, r19
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st X, r2
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inc r1
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brne 2b
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pop r2
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pop r28
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pop r29
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ret
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/*
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uint8_t arcfour_gen(arcfour_ctx_t *c){
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uint8_t t;
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c->i++;
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c->j += c->s[c->i];
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t = c->s[c->j];
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c->s[c->j] = c->s[c->i];
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c->s[c->i] = t;
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return c->s[(c->s[c->j] + c->s[c->i]) & 0xff];
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}
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*/
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.global arcfour_gen
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;== arcfour_gen ==
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; this function initialises the context
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; param1: 16-bit pointer to a ctx struct
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; given in r25,r24
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arcfour_gen:
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movw r26, r24
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ld r18, X
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inc r18
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st X+, r18
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movw r30, r26
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ld r19, X+
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add r26, r18
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adc r27, r1
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ld r20, X
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add r19, r20
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st Z+, r19 /* i,j loaded&saved; X->S[i]; Z->S[0]; r20=S[i] */
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add r30, r19
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adc r31, r1
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ld r21, Z /* X->S[i]; Z->S[j]; r20=S[i]; r21=S[j]*/
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st Z, r20
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st X, r21
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add r20, r21
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adiw r24, 2
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movw r26, r24 /* X and Z point to S */
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add r26, r20
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adc r27, r1
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ld r24, X
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clr r25
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ret
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