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Ohm

Hint: CRYPT001

5 posts in this topic

So here's a generic hint of these types of things: spot the encoding.

  • ASCII encoding is easy to spot. You're seeing it right now. It's generally limited to representing text that can be typed.
  • Hex encoding will consist of digits 0-9 and A-F, sometimes lowercase a-f. Each hex digit represents 4 bits of the text, so the hex string will be twice as long as the message. This is a simplistic encoding used in low-level applications, or applications where the binary value of the message needs to be read or manipulated by humans. Also, it's sometimes preceded by 0x. It looks like 0x4d657373616765.
  • Base64 encoding is used to represent binary data in ASCII form. It's more efficient than hex, encoding 6 bits per byte rather than 4 bits as with hex. It uses all 26 letters in both upper-case and lower-case form (that's 26 + 26 = 52 characters) and the digits 0 - 9, as well as + and / (for a total of 64 characters). Finally, the message is padded to a multiple of 3 bytes with the = character. Base64 looks like TWVzc2FnZQo=
  • URL encoded strings encode characters that would have special meaning in URLs (?, &, #, etc) using a %xx format, where xx is the hex of the ASCII value. A common one you may see is %20 in URLs, representing a space.
  • HTML entities are used to escape special characters in HTML code. It looks like &, followed by either an identifier specified in the HTML specs or a number, then a ; character. For example, > and < can be used to represent the < and > characters. Or you can use the ASCII values in decimal like < and > for < and >.
  • MD5 hashes are usually represented in hex format and are 128 bits (32 hex characters) long. They look like 4c2a8fe7eaf24721cc7a9f0175115bd4.
  • SHA1 hashes are 160 bits long (40 hex characters). They look like 68f4145fee7dde76afceb910165924ad14cf0d00

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I guess it's time for a second hint. As you seem to have figured out, it is base64 encoded. This simple "encryption" takes advantage of the fact that base64 encodes only 6 bits per byte. It's also simpler than you may think.

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So I guess it's time for one last hint. It's so simple, you'll kick yourself. What happens if you remove or inject a character into the base64 character stream?

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I did kick myself, I guess I was trying to much of the stuff I used to solve the crypto puzzles at hacker.org

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it contains the phrase : secret message :P

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