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logicog
85244d85f9
Add an implementation in 8051 assembler for the generation of a ChaCha20 keystream and an encryption function using the keystream in C. A test function using the example from RFC7539 is provided in chacha20_test. Keys, nonce, and block counter and the pointers to the input plaintext, its length and the output pointer are provided via a struct chacha20, which also holds the working state of the ChaCha20 algorithm
99 lines
2.8 KiB
C
99 lines
2.8 KiB
C
#include "rtl837x_common.h"
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#include "chacha.h"
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void chacha_20(void);
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void chacha_update(void);
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void chacha_count(void);
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// generate a block of ChaCha20 keystream as per RFC7539
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__xdata struct chacha20_t __at(0x7000) chacha20;
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__xdata uint8_t plaintext[256];
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__xdata uint8_t cyphertext[256];
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void chacha20_print_block(void)
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{
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for (uint8_t i=0; i < 64; i++) {
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print_byte(*(uint8_t * __xdata)(chacha20.wstate + i));
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if (i%4 == 3)
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write_char(' ');
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}
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}
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void chacha20_encrypt(void)
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{
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__xdata uint8_t *p = chacha20.plaintext;
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while (chacha20.length) {
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register uint8_t i;
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chacha_count();
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memcpy(chacha20.wstate, chacha20.wstate + 64, 64);
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#ifdef DEBUG
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chacha20_print_block(); write_char('\n');
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#endif
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chacha_20();
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chacha_update();
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#ifdef DEBUG
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chacha20_print_block(); write_char('\n');
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#endif
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for (i = 0; i < ((chacha20.length > 64) ? 64 : chacha20.length); i++)
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*chacha20.cyphertext++ = *p++ ^ chacha20.wstate[i];
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chacha20.length -= chacha20.length > 64 ? 64 : chacha20.length;
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#ifdef DEBUG
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print_string("\n round done\n");
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#endif
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};
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}
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// Test the example of RFC 7539 Section 2.4.2
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void chacha20_test(void)
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{
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__code uint8_t chacha_c[16] =
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{ 0x61, 0x70, 0x78, 0x65, 0x33, 0x20, 0x64, 0x6e,
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0x79, 0x62, 0x2d, 0x32, 0x6b, 0x20, 0x65, 0x74 };
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__code uint8_t key[32] =
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{ 0x03, 0x02, 0x01, 0x00, 0x07, 0x06, 0x05, 0x04,
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0x0b, 0x0a, 0x09, 0x08, 0x0f, 0x0e, 0x0d, 0x0c,
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0x13, 0x12, 0x11, 0x10, 0x17, 0x16, 0x15, 0x14,
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0x1b, 0x1a, 0x19, 0x18, 0x1f, 0x1e, 0x1d, 0x1c };
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__code uint8_t nonce[12] = {
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0x00, 0x00, 0x00, 0x00, 0x4a, 0x00, 0x00, 0x00,
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0x00, 0x00, 0x00, 0x00 };
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__code uint8_t sunscreen[] = "Ladies and Gentlemen of the class of '99: If I could offer you only one tip for " \
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"the future, sunscreen would be it.";
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/*
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Ciphertext Sunscreen (from RFC 7539 Section 2.4.2):
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000 6e 2e 35 9a 25 68 f9 80 41 ba 07 28 dd 0d 69 81 n.5.%h..A..(..i.
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016 e9 7e 7a ec 1d 43 60 c2 0a 27 af cc fd 9f ae 0b .~z..C`..'......
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032 f9 1b 65 c5 52 47 33 ab 8f 59 3d ab cd 62 b3 57 ..e.RG3..Y=..b.W
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048 16 39 d6 24 e6 51 52 ab 8f 53 0c 35 9f 08 61 d8 .9.$.QR..S.5..a.
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064 07 ca 0d bf 50 0d 6a 61 56 a3 8e 08 8a 22 b6 5e ....P.jaV....".^
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080 52 bc 51 4d 16 cc f8 06 81 8c e9 1a b7 79 37 36 R.QM.........y76
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096 5a f9 0b bf 74 a3 5b e6 b4 0b 8e ed f2 78 5e 42 Z...t.[......x^B
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112 87 4d
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*/
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strcpy(plaintext, sunscreen);
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memcpyc(chacha20.constant, chacha_c, 16);
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memcpyc(chacha20.key, key, 32);
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chacha20.cnt = 0;
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memcpyc(chacha20.nonce, nonce, 12);
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chacha20.plaintext = plaintext;
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chacha20.length = strlen_x(plaintext);
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chacha20.cyphertext = cyphertext;
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print_string("Encrypting...\n");
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chacha20_encrypt();
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print_string("Cypertext:\n");
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uint16_t len = strlen_x(plaintext);
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for (uint8_t i = 0; i < len; i++) {
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print_byte(cyphertext[i]); write_char(' ');
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}
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}
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