How to Decode Base64 Strings
Base64 is a common method of information exchange between computers. Designed to prevent data tampering by intermediate systems, it encodes information using simple ASCII characters. The key to decoding Base64 is to understand that it encodes 3 bytes into four 6-bit chunks.
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Instructions
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1
Read 4 bytes from the string. If there is only 1 byte left, the input is corrupted or invalid. If there are 2 or 3 bytes left, pad the string with "=" characters until it is 4 bytes.
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2
Find the 6-bit representation of each byte and put them next to each other so they form a 24-bit value. Letters A to Z have values 0 to 25, a to z have values 26 to 51, numerals 0 to 9 have values 52 to 61, while "+" has 62 and "/" has 63. If you come across an "=" symbol, stop processing the string and go to the next step.
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3
Break the resulting bits into 8-bit groups. Each full 8-bit group represents 1 byte of the original unencoded string. If there were "=" symbols, you would end up with extra bits that do not make a full 8-bit value. Discard these.
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4
Repeat the entire process until there are no more characters left in the string.
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