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Password Cracker

Problem

Whilst surfing you happen to stumble upon a "hackers" website that is part of a ring of thirteen; each site linking to the next one, until returning to the first. Curiously one of them requires a password and as you cycle through the front pages of the other twelve you notice some strange figures in the bottom right corner. It was not obvious, because each time the web page designer has chosen a colour only slightly different to the background.

Assuming that the password protected site is the last in the ring, you write down the codes from each site sequentially to form a string.

706173733D4861636B65725A

Can you unlock the password?


Solution

The string is made up of 12 hexadecimal bytes (base 16): 70, 61, 73, 73, 3D, 48, 61, 63, 6B, 65, 72, 5A.

Each hexadecimal digit has the following value: 0=0, 1=1, ... , 8=8, 9=9, A=10, B=11, C=12, D=13, E=14, F=15. Similar to decimal (base 10), the first digit in any 2-digit number (reading right to left) is units, but the second digit is 16's (compare with 10's, 100's, 1000's, et cetera).

So the hexadecimal number 5A, the last byte in the message, is worth 5 times 16 + 10 = 90.

By converting the hexadecimal bytes to decimal, we form the following string of decimal numbers: 112, 97, 115, 115, 61, 72, 97, 99, 107, 101, 114, 90.

These represent the ASCII (American Standard Code for Information Interchange) codes for the characters in the message. A brief introduction to ASCII can be found in the FAQ section. Alternatively you could do a search for character/ASCII code conversion tables on the internet, ascii table (Google search link). For example, the character for ASCII code 90 is Z (capital). Note that some tables will list the corresponding character values in hexadecimal, so converting to decimal may not be necessary.

By converting the string we read the message: pass=HackerZ.

What is the advantage of using hexadecimal?
Investigate the way in which characters have been mapped.

For example, is it a coincidence that the ASCII codes for 1, 2, 3, ..., are at 31, 32, 33, ... (hex); A, B, C, ..., start at 41 and a, b, c, ... start at 61?

Problem ID: 7 (Aug 2000)     Difficulty: 2 Star

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