Cryptography Reference
In-Depth Information
1 /* crack vigenere ciphers by statistical methods
2
(C) Reinhard Wobst, Dresden (Germany) @(#) 30.Oct 22:57, 1996
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Usage: vigcrack distr_file <crypted_file
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The 'distr_file' must be generated by the program 'distr' from
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a typical plaintext:
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distr <plaintext >distr_file
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The file plaintext must have typical character frequencies.
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Not applicable for equally distributed plaintexts (gzip etc).
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Output: One proposed keyword, trust value (the higher, the
better).
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A trust value near 1 indicates insecure password detection.
11 */
12 #include <stdio.h>
13 #include <ctype.h>
14 #include <memory.h>
15 #define MAXPERIOD
64
/* max. key length */
16 #define MAXLEN
40960
/* max. portion of read source */
17 #define THRESH
0.1
/* "threshold factor for max.
probability" */
18 #define PERC
0.01
/* 1% - kappa (coeff. of coincidence)
*/
19 main(argc, argv)
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char *argv[];
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{
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unsigned char buf[MAXLEN], key[MAXPERIOD+1],
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*p;
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register n, m;
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int n0, c, off, indx, period, kappacnt, N, Np,
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cnt[256];
Figure 3.13:
Using
vigcrack
to break a Vigenere cipher.
