33 lines
1.3 KiB
Plaintext
33 lines
1.3 KiB
Plaintext
;Task:
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Write a program that takes a [[wp:bitcoin|bitcoin address]] as argument,
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and checks whether or not this address is valid.
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A bitcoin address uses a base58 encoding, which uses an alphabet of the characters 0 .. 9, A ..Z, a .. z, but without the four characters:
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:::* 0 zero
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:::* O uppercase oh
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:::* I uppercase eye
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:::* l lowercase ell
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With this encoding, a bitcoin address encodes 25 bytes:
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* the first byte is the version number, which will be zero for this task ;
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* the next twenty bytes are a [[RIPEMD-160]] digest, but you don't have to know that for this task: you can consider them a pure arbitrary data ;
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* the last four bytes are a checksum check. They are the first four bytes of a double [[SHA-256]] digest of the previous 21 bytes.
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To check the bitcoin address, you must read the first twenty-one bytes, compute the checksum, and check that it corresponds to the last four bytes.
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The program can either return a boolean value or throw an exception when not valid.
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You can use a digest library for [[SHA-256]].
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;Example of a bitcoin address:
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<big>
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1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i
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</big>
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It doesn't belong to anyone and is part of the test suite of the bitcoin software.
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<br>You can change a few characters in this string and check that it'll fail the test.
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<br><br>
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