8/12/2023 0 Comments Base64 decode linux![]() ![]() ![]() Below I'm showing where the Q comes from when you re-encode the data. Philip Couling explains the intricacies of the decoding of the final ld= part and that, in a way, only a third of the data encoded by the d is actually used when decoding the data. This is the data that HelloWorld= is the base64 encoding of. Yes, it's an interaction with the padding. That is the only valid endings with = are Q= A= w= g= So when you decode your string with base64 -d, only 100101 01 will be converted into a byte and the end 1101 will be ignored completely.Īny base 64 string ending in = must only use the first two bits of the last character. Ld= should decode to only one byte because it has two = at the end. ![]() To understand why see this lookup table: In your example Hell and oWor are both valid. Base64 strings will always be divisible by 4. The only exception is the last 4 characters which will vary depending on the number of = signs. Each character represents 6 bits, so each group of 4 decodes into 3 bytes (8 bits per byte). The extra 1s this contains will be ignored and lost when you echo "HelloWorld=" | base64 -d.īase64 Works with groups of 4 characters. HelloWorld= contains information which cannot be decoded, and isn't technically valid Base64 since they should in general be 0 padded. ![]()
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