Dialog Options for the attack on the hash value of the digital signature

You can access this dialog by clicking the Options button in the Attack on the hash value of the digital signature dialog.

First, one of six hash functions hash functions can be chosen for the attack. The 128-bit hash functions MD2, MD4 and MD5 as well as the 160-bit hash functions SHA, SHA-1 and RIPEMD-160 are available.

The Significant bit length determines the number of the highest bits in the hash values that have to match so that the attack is considered successful. The co-domain of the significant bit length is 1 <= x <= n, with n being the bit length of the chosen hash function.

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In the category Options for the modification of messages the method of modifying messages depending on the lastly computed hash value can be chosen.

If the radio button Insert blanks is checked, at least one of the two check boxes In front of end of line and Double Blanks has to be checked. Starting from the end of a message, a blank is inserted in front of an end of line and/or in front of another blank.

Attach characters is the other method of modifying messages. There, two bits of a hash value are mapped on one character which is attached at the end of the message. For reasons of demonstration, Printable characters ("A", "B", "C" or "D") can be used, otherwise Unprintable characters (the characters with the ASCII codes 9, 10, 32 or 160) are attached.

With Reset to standard the settings are reset to:

Hash function: MD2
Significant bit length: 16
Method of modification: Insert blanks/In front of end of line and Double Blanks

By clicking Apply the current settings are saved in the file CrypTool.INI and used for all attacks in the future, besides, the user returns to the dialog Attack on the hash value of the digital signature.

Remark: If you choose in the first group of the options dialog a significant bit length such, that the function will have a long duration (e.g. n > 40), another dialog with a progress indicator appears.