diff options
| -rw-r--r-- | lib/lib.c | 473 | ||||
| -rw-r--r-- | lib/lib.h | 27 | ||||
| -rw-r--r-- | lib/lib2.c | 23 | ||||
| -rw-r--r-- | lib/lib2.h | 11 | ||||
| -rw-r--r-- | set2/Makefile | 10 | ||||
| -rw-r--r-- | set2/task9.c | 14 |
6 files changed, 558 insertions, 0 deletions
diff --git a/lib/lib.c b/lib/lib.c new file mode 100644 index 0000000..c2ee753 --- /dev/null +++ b/lib/lib.c @@ -0,0 +1,473 @@ + +#include "lib.h" + +static const unsigned char base64_encode[] = + "ABCDEFGHIJKLMNOPQRSTUVWXYZ" + "abcdefghijklmnopqrstuvwxyz" + "0123456789+/"; + + +static const unsigned char hex_encode[] = + "0123456789abcdef"; + + + +/** + * teset wheter a bit on the given position is 1 + */ +static int bit_on(char test, int bit) +{ + char tmp; + tmp = 1 << bit; + tmp = test & tmp; + + return (int) tmp; +} + + +/** + * returns true if the given string contains only printable or whitespace + * characters + */ +int isprintable(char *string, int length) +{ + int i; + + for(i=0;i<length;i++) { + if(!(isprint(string[i]) || isspace(string[i]))) { + return 0; + } + } + + return 1; +} + + +/* + * task the first three characters of encode and tranform it into the coresponding + * for bytes in base64 and stores it in result +*/ +static void three_bytes_to_base64(char * encode, int bytes_to_print, char *result) +{ + unsigned char one, two, three, four; + unsigned char tmp; + char ret[4]; + + // first six bits + one = encode[0] >> 2; + ret[0] = base64_encode[one]; + if(bytes_to_print-- > 0) + result[0] = ret[0]; + // second six bits + // two last bits of first byte + tmp = encode[0] & 0x03; + two = encode[1] >> 4; + tmp = tmp << 4; + two = tmp | two; + ret[1] = base64_encode[two]; + if(bytes_to_print-- > 0) + result[1] = ret[1]; + // second six bits + // two last bits of first byte + // third six bits + tmp = encode[1] & 0x0F; + tmp = tmp << 2; + three = encode[2] & 0xC0; + three = three >> 6; + three = tmp | three; + ret[2] = base64_encode[three]; + if(bytes_to_print-- > 0) + result[2] = ret[2]; + // last six bit11s + four = encode[2] & 0x3F; + ret[3] = base64_encode[four]; + ret[4] = '\0'; + if(bytes_to_print-- > 0) + result[3] = ret[3]; +} + +void print_char_bit(char print) +{ + int i; + for(i=0;i<8;i++) { + if (bit_on(print,i)) + printf("1"); + else + printf("0"); + } +} +/** + * Transform four base64 encoded characters back to three bytes + */ + +const char decodeCharacterTable[256] = { + -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1 + ,-1,62,-1,-1,-1,63,52,53,54,55,56,57,58,59,60,61,-1,-1,-1,-1,-1,-1,-1,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21 + ,22,23,24,25,-1,-1,-1,-1,-1,-1,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,-1,-1,-1,-1,-1, + -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1, + -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1 + ,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1, + -1,-1,-1 +}; + + +void decode_four_base64_byte(char *string1, char *result) +{ + char buf[4]; + + // map the bytes back to the orginial bitmap + // A = 0 + buf[0] = decodeCharacterTable[(int)string1[0]]; + buf[1] = decodeCharacterTable[(int)string1[1]]; + buf[2] = decodeCharacterTable[(int)string1[2]]; + buf[3] = decodeCharacterTable[(int)string1[3]]; + + // first byte is first six bits of base64 one and 2 bit of base64 second + result[0] = ((buf[0] << 2) & 0xFC) | ((buf[1] >> 4) & 0x03); + + // second byte 4 bits of second base64 + 4 bits of third base64 + result[1] = ((buf[1] << 4) & 0xF0) | ((buf[2] >> 2) & 0x0F); + + // third byte 2 bits of third base54 + 6 bits of fourth base64 + result[2] = ((buf[2] & 0x03) << 6) | (buf[3] & 0x3F); + +} + + +int decode_base64(char *string1, char *result) +{ + int i, j, padding; + + for(i=0, j=0;i<strlen(string1);i += 4, j +=3) { + decode_four_base64_byte(&string1[i], &result[j]); + } + + // handle padding in the last four bytes + i -= 4; + + for(padding=0;i<strlen(string1);i++) { + if (string1[i] == '=') + padding++; + } + + result[j-padding] = '\0'; + + return (j-padding); + +} + +static char string_to_hex_map[] = {0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, + 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, + 0x0E, 0x0F}; +/* + * This function converts the first char of a string into its corresponding + * hex value + * + * @return on Sucess return 0, if char is no valid hex value returns -1 + */ +static int hex_char_to_bit(char toEncode) +{ + char encode; + switch(toEncode) { + case '0': + encode = string_to_hex_map[0]; + break; + case '1': + encode = string_to_hex_map[1]; + break; + case '2': + encode = string_to_hex_map[2]; + break; + case '3': + encode = string_to_hex_map[3]; + break; + case '4': + encode = string_to_hex_map[4]; + break; + case '5': + encode = string_to_hex_map[5]; + break; + case '6': + encode = string_to_hex_map[6]; + break; + case '7': + encode = string_to_hex_map[7]; + break; + case '8': + encode = string_to_hex_map[8]; + break; + case '9': + encode = string_to_hex_map[9]; + break; + case 'a': + encode = string_to_hex_map[10]; + break; + case 'b': + encode = string_to_hex_map[11]; + break; + case 'c': + encode = string_to_hex_map[12]; + break; + case 'd': + encode = string_to_hex_map[13]; + break; + case 'e': + encode = string_to_hex_map[14]; + break; + case 'f': + encode = string_to_hex_map[15]; + break; + default: + return -1; + } + + return encode; + +} + +/** + * takes the first two hex characters of start and convert them to one byte + * with the coressponding value of the two hex chars + */ +static void two_char_hex(char *start, char *result) +{ + char first = hex_char_to_bit(start[0]); + char second = hex_char_to_bit(start[1]); + + *result = first; + *result = *result << 4; + *result = *result | second; +} + +/** + * xor agianst a key. if the length of key is less than the length of + * str1 than the key will be repeated + * @param str1 string which should be xored agianst the given key + * @param key + * @param result buffer where the result is stored + */ +void xor_string(char *str1, char *key, char *result, int length_key, int length_str1) +{ + int i, j; + //int length_key = strlen(key); + + for(i=0, j=0;i<length_str1;i++,j++) { + if (j >= length_key) + j = 0; + + result[i] = str1[i] ^ key[j]; + } + + result[i] = '\0'; +} + + +/** + * transform the bytes in str1 into its correspond printable hex version + * @param str1 binary strewam which should be converted + * @param result buffer where the results should be stored + * @param length legnth of str1 + */ +void hex_binary_to_string(char *str1, char *result, int length) +{ + int i, j, tmp = 0; + + for(i=0,j=0;i<length;i++, j+=2) { + tmp = str1[i] & 0xF0; + tmp = tmp >> 4; + result[j] = hex_encode[tmp]; + tmp = str1[i] & 0x0F; + result[j+1] = hex_encode[tmp]; + } + + result[j] = '\0'; +} + +/** + * takes a hex string and converts it to its correspond binary counterpart + */ +int decode_hex_string(char *encode, char* result) +{ + int i; + int length = strlen(encode); + + for(i = 0;i< length/2;i++) + two_char_hex(&encode[i*2], &result[i]); + + return i; +} + +/** + * counts the frequent characters in a string an divide the number through the + * total number of characters + * @param string string where the frequent characters should be counted + * @param length length of string + */ + +static int frequent_histogramm_matchs(char *string, int length) +{ + int i; + int hits = 0; + char tmp; + int number_frequent_characters[14] = { 0, 0, 0, 0, 0, 0, 0, 0 ,0 ,0 ,0 ,0, 0, 0}; + // frequent characters: + // a c d e h i l m n o r s t u w + double standard_frequencies[14] = { 8.1, 2.7, 4.2, 12.7, 6.0, 6.9, 4.0, 2.4, 6.7, 7.5, 5.9, 6.3, 9.0, 2.7 }; + + // count frequent characters + for(i=0;i<length;i++) { + tmp = tolower(string[i]); + switch(tmp) { + case 'a': + number_frequent_characters[0]++; + break; + case 'c': + number_frequent_characters[1]++; + break; + case 'd': + number_frequent_characters[2]++; + break; + case 'e': + number_frequent_characters[3]++; + break; + case 'h': + number_frequent_characters[4]++; + break; + case 'i': + number_frequent_characters[5]++; + break; + case 'l': + number_frequent_characters[6]++; + break; + case 'm': + number_frequent_characters[7]++; + break; + case 'n': + number_frequent_characters[8]++; + break; + case 'o': + number_frequent_characters[9]++; + break; + case 'r': + number_frequent_characters[10]++; + break; + case 's': + number_frequent_characters[11]++; + break; + case 't': + number_frequent_characters[12]++; + break; + case 'u': + number_frequent_characters[13]++; + break; + } + } + #define FREQ_AREA 0.7 + // compare frequncies with standard frequencies + for(i=0;i<14;i++) { + double freq =(double) ((double)number_frequent_characters[i]*100/(double)length); + if((((standard_frequencies[i] * (1-FREQ_AREA) < freq) + )&& ((standard_frequencies[i] * (1+FREQ_AREA)) > freq))) { + hits++; + } + } + return hits; +} + +/** + * encode the given string into base64 and stores it in result + */ + +void encode_to_base64(char *encode, char *result) +{ + int length = strlen(encode); + + int rounds = length / 3; + int bytes_last_round = length % 3; + int i; + + for (i=0;i<rounds;i++) { + three_bytes_to_base64(encode + i*3,4, &result[i*4]); + } + // in der letzen runde nicht mehr alle ausgeben + // nur noch 3-leftover + if (bytes_last_round > 0) { + three_bytes_to_base64(encode + i*3, 1+bytes_last_round, &result[i*4]); + + for(i=0;i<(3-bytes_last_round);i++) + result[i*4+(1+bytes_last_round)] = '='; + } + +} + +/** + * prints and base64 encoded string + */ +void print_base64_string(char *string) +{ + // after 76 charactes line break + +} + +/** + * compute the hamming distance (number of different bits) of two string + * @param string1 first string + * @parma string2 second string + * @return returns the hamming distance + */ +int hamming_distance_equal_length(char *string1, char *string2, int length) +{ + char tmp; + int i, j; + int hamming_distance = 0; + + for(i=0;i<length;i++) { + tmp = string1[i] ^ string2[i]; + for(j = 0; j < 8; j++) { + if (bit_on(tmp, j)) + hamming_distance++; + } + } + return hamming_distance; +} + +/** + * test every byte on the string as key and returns the found keys + */ +char brute_force_single_byte_xor(char *string, int length, struct key_and_freq *ret) +{ + int i; + char *xor_tmp; + char single_byte_key; + char key = 'A'; + int max_hits = 0; + int tmp_hits = 0; + + xor_tmp = malloc(length+1); + +// printf("NEW STINGT TO BREAK\n"); + // test for every byte + for(i=1;i<255;i++) { + single_byte_key = (char) i; + xor_string(string, &single_byte_key, xor_tmp, 1, length); + + // if string contains not printable characters it is not + // the cleartext + if (!isprintable(xor_tmp, length)) + continue; + + tmp_hits = frequent_histogramm_matchs(xor_tmp, length); + + if (tmp_hits > max_hits) { + max_hits = tmp_hits; + key = single_byte_key; + //printf("Key: %c, hits: %i\n", key, max_hits); + } + + } + + ret->key = key; + ret->hits= max_hits; + + return key; +} diff --git a/lib/lib.h b/lib/lib.h new file mode 100644 index 0000000..3e2a309 --- /dev/null +++ b/lib/lib.h @@ -0,0 +1,27 @@ +#ifndef __CRYPTO_LIB__ +#define __CRYPTO_LIB__ + + +#include <stdio.h> +#include <string.h> +#include <stdlib.h> +#include <ctype.h> + +struct key_and_freq { + char key; + int hits; +}; + +void print_char_bit(char); +void xor_string(char *str1, char *key, char *result, int length_key, int length_str1); +void hex_binary_to_string(char *str1, char *result, int length); +int decode_hex_string(char *encode, char* result); +void encode_to_base64(char *encode, char *result); +int decode_base64(char *string1, char *result); +void print_base64_string(char *string); +int hamming_distance_equal_length(char *string1, char *string2, int length); +char brute_force_single_byte_xor(char *string, int length, struct key_and_freq *tmp); +int isprintable(char *string, int length); + + +#endif /* __CYRPTO_LIB__ */ diff --git a/lib/lib2.c b/lib/lib2.c new file mode 100644 index 0000000..86dd823 --- /dev/null +++ b/lib/lib2.c @@ -0,0 +1,23 @@ +#include "lib2.h" + +/** + * appends PKCS#7 padding to string. devide string in blocks of size blocksize + * and append to last block so that it is also of blocksize length + */ + +char *pkcs7_padding(char *string, int length_string, int blocksize) +{ + char *result = NULL; + int i; + int value = blocksize - (length_string % blocksize); + + result = malloc(length_string+value+1); + memcpy(result, string, length_string); + + for(i=0;i<value;i++) { + result[length_string+i] = (char) value; + } + result[length_string+i] = '\0'; + + return result; +} diff --git a/lib/lib2.h b/lib/lib2.h new file mode 100644 index 0000000..818558d --- /dev/null +++ b/lib/lib2.h @@ -0,0 +1,11 @@ +#ifndef __LIB2_H__ +#define __LIN2_H__ + +#include <stdio.h> +#include <string.h> +#include <stdlib.h> + +char *pkcs7_padding(char *string, int length_string, int blocksize); + + +#endif diff --git a/set2/Makefile b/set2/Makefile new file mode 100644 index 0000000..abbacc0 --- /dev/null +++ b/set2/Makefile @@ -0,0 +1,10 @@ +LIB=../lib/lib2.c +CC=gcc +CFLAGS := -g -Wall $(CFLAGS) + +all: task9 + +task9: + $(CC) $(CFLAGS) task9.c $(LIB) -o task9 +clean: + rm task9 diff --git a/set2/task9.c b/set2/task9.c new file mode 100644 index 0000000..9b91174 --- /dev/null +++ b/set2/task9.c @@ -0,0 +1,14 @@ +#include "../lib/lib2.h" +#include <stdio.h> + +int main(int argc, char **argv) +{ + // implemten PKCS#7 padding + char *result = NULL; + + result = pkcs7_padding("YELLOW SUBMARINE", 16, 10); + printf("%s\n", result); + + free(result); + return 0; +} |