mirror of https://github.com/dirtbags/moth.git
65 lines
2.1 KiB
Markdown
65 lines
2.1 KiB
Markdown
Tokens
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======
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Tokens are good for a single point in a single category. They are
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formed by prepending the category and a colon to the bubblebabble digest
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of 3 random octets. A token for the "merfing" category might look like
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this:
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merfing:xunap-motex
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Entropy
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-------
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3 octets provides 24 bits of entropy. This gives 16777216 possible
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tokens in each category. The longest contest yet run lasted 24 hours,
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which would give 2^24/24/60 = 11650 tokens per category per minute. I
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think this is a large enough pool to discourage brute-force attacks.
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Assuming /dev/urandom is as good as is claimed, brute-force would be the
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only way to attack it.
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Token server
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------------
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Sometimes it's a good idea to have certain puzzles run on a different
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machine than the server. For instance, something that loads down the
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CPU, or something that carries a high risk of local exploit. The token
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server listens on TCP port 1, issuing tokens encrypted with ARC4
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(symmetric encryption). Here's how the transaction goes:
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C: category
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S: nonce (4 bytes)
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C: nonce encrypted with symmetric key
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S: token encrypted with symmetric key
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Token client
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------------
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The token client (in package "tokencli") runs as a daemon, requesting a
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new token every minute for each puzzle. Because we want you to have
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multiple puzzles within a category, and the server only knows about
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categories, each puzzle needs to be associated with a category.
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Additionally, tokens are encrypted before being written to the local
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filesystem, with a different key for each puzzle.
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The token client thus needs a 4-tuple for each puzzle:
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(puzzle name, puzzle key, category, category key)
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In the interest of making things easy to administer and code, this
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4-tuple is stored in files and directories:
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/packages/packagename/tokencli/puzzle_name/enc.key
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/packages/packagename/tokencli/puzzle_name/category.key
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/packages/packagename/tokencli/puzzle_name/category
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And puzzles are stored in:
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/state/tokens/puzzle_name
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Using this scheme, the token client has only to iterate over
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/packages/*/tokencli/* instead of implementing some sort of parser.
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