dimitri/cryptopals
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Refactor frequency analysis

Browse source
This commit is contained in:
Dimitri Lozeve 2020-06-03 19:20:26 +02:00
parent 5a30f34558
commit 2503961778
4 changed files with 29 additions and 27 deletions
Download patch file Download diff file Expand all files Collapse all files

26
ex03/main.c
View file

@ -1,33 +1,9 @@
#include "utils.h"
#include <ctype.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
double frequency_score(unsigned char *buf, size_t len) {
static const double english_freqs[26] = {
0.08167, 0.01492, 0.02782, 0.04253, 0.12702, 0.02228, 0.02015, // A-G
0.06094, 0.06966, 0.00153, 0.00772, 0.04025, 0.02406, 0.06749, // H-N
0.07507, 0.01929, 0.00095, 0.05987, 0.06327, 0.09056, 0.02758, // O-U
0.00978, 0.02360, 0.00150, 0.01974, 0.00074 // V-Z
};
unsigned int counts[26] = {0};
for (size_t i = 0; i < len; ++i) {
unsigned char c = tolower(buf[i]) - 'a';
if (c < 26) {
counts[c]++;
}
}
double chi2 = 0;
for (size_t i = 0; i < 26; ++i) {
double expected = len * english_freqs[i];
chi2 += pow(counts[i] - expected, 2) / expected;
}
return chi2;
}
#include <math.h>
int main(int argc, char *argv[]) {
if (argc < 2) {

4
meson.build
View file

@ -3,6 +3,6 @@ project('cryptopals', 'c')
cc = meson.get_compiler('c')
m_dep = cc.find_library('m', required : false)
executable('ex01', ['ex01/main.c', 'utils.c'])
executable('ex02', ['ex02/main.c', 'utils.c'])
executable('ex01', ['ex01/main.c', 'utils.c'], dependencies: m_dep)
executable('ex02', ['ex02/main.c', 'utils.c'], dependencies: m_dep)
executable('ex03', ['ex03/main.c', 'utils.c'], dependencies: m_dep)

25
utils.c
View file

@ -1,5 +1,6 @@
#include "utils.h"
#include <ctype.h>
#include <math.h>
#include <string.h>
unsigned char hex_to_byte(const char c) {
@ -35,3 +36,27 @@ unsigned char *bytes_to_base64(unsigned char *out,
}
return out;
}
double frequency_score(unsigned char *buf, size_t len) {
static const double english_freqs[26] = {
0.08167, 0.01492, 0.02782, 0.04253, 0.12702, 0.02228, 0.02015, // A-G
0.06094, 0.06966, 0.00153, 0.00772, 0.04025, 0.02406, 0.06749, // H-N
0.07507, 0.01929, 0.00095, 0.05987, 0.06327, 0.09056, 0.02758, // O-U
0.00978, 0.02360, 0.00150, 0.01974, 0.00074 // V-Z
};
unsigned int counts[26] = {0};
for (size_t i = 0; i < len; ++i) {
unsigned char c = tolower(buf[i]) - 'a';
if (c < 26) {
counts[c]++;
}
}
double chi2 = 0;
for (size_t i = 0; i < 26; ++i) {
double expected = len * english_freqs[i];
chi2 += pow(counts[i] - expected, 2) / expected;
}
return chi2;
}

1
utils.h
View file

@ -7,5 +7,6 @@ unsigned char hex_to_byte(const char c);
size_t hex_to_bytes(unsigned char *out, const char hex[static 1]);
unsigned char *bytes_to_base64(unsigned char *out,
const unsigned char in[static 1], size_t len);
double frequency_score(unsigned char *buf, size_t len);
#endif /* UTILS_H */