June 2018 Update

Task/Bitcoin-address-validation/00DESCRIPTION

@@ -1,26 +1,36 @@
 {{omit from|Brlcad}}
 {{omit from|GUISS}}
 
+
+;Task:
 Write a program that takes a [[wp:bitcoin|bitcoin address]] as argument,
 and checks whether or not this address is valid.
 
-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 0, O, I and l.
+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:
+:::*   0   zero
+:::*   O   uppercase oh
+:::*   I   uppercase eye
+:::*   l   lowercase ell
+
 
 With this encoding, a bitcoin address encodes 25 bytes:
 * the first byte is the version number, which will be zero for this task ;
 * 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 ;
 * 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.
 
+
 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.
 
 The program can either return a boolean value or throw an exception when not valid.
 
 You can use a digest library for [[SHA-256]].
 
-Here is an example of a bitcoin address:
 
-1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i
+;Example of a bitcoin address:
+<big>
+ 1AGNa15ZQXAZUgFiqJ2i7Z2DPU2J6hW62i
+</big>
 
-It does not belong to anyone.
-It is part of the test suite of the bitcoin software.
-You can change a few characters in this string and check that it will fail the test.
+It doesn't belong to anyone and is part of the test suite of the bitcoin software.
+<br>You can change a few characters in this string and check that it'll fail the test.
+<br><br>