When using my programs you will see these conversions are in nearly every source code.
The answer is very simple: because all types of cryptography are working with binary data but when trying to transport the data (e.g. a ciphertext) from one system to another system you encounter the problem - "how should I transport binary data?".
As binary data can consist of bytes that are not directly printable as a string (e.g. value hex x00) we need to convert the data to a better (string) encoding. In general there are two encodings on the market - the Base64 encoding and the hex string representation of the binary data.
This article focuses on the Base64 encoding, if you like to know more about the hex string representation of binary data see my article binary data to a hex string & back.
A byte can hold up to 256 values that need to find a string representation. When trying to use only the letters a..z, A..Z and numbers 0..9 and 3 extra symbols like "/", "+" and "=" we get a character set of (in total) 65 characters - much to low for the necessary 256 characters. So trick is not to use the 8 bit of byte but only 6 bit of the byte sequence, convert this 6 bit chunk into a character of the set and in the end all bytes get converted.
This procedure will exand the length of encoded data about 33% but those characters are available on nearly every western operating system. The decoding goes the other way round and there is the "problem" with a padding that is done with the "=" character because not all byte sequences are divisible by "6".
If need more detailed information about this process kindly see the Wikipedia Base64 article.
This is a serious warning regarding the security of the programs shown in these article series. Always keep in mind my disclaimer regarding my programs: All programs are for educational purposes and are not intended to use in production or any other programs where a secure solution is needed. The programs do not have proper exceptional/error handling and in some cases they use insecure key lengths or other methods that are insecure. Never ever use the programs in real life unless checked by a qualified professional cryptographer.
The following links provide the solution in code and within an online compiler that runs the code. Kindly note that three articles use the same example: Base64 encoding & decoding, binary data to a hex string & back and SHA256 hashing.
*1) you need the external library pointycastle version 3.1.1
This is an output:
Generate a SHA-256 hash, Base64 en- and decoding and hex conversions
plaintext: The quick brown fox jumps over the lazy dog
sha256Value (hex) length: 32 data: d7a8fbb307d7809469ca9abcb0082e4f8d5651e46d3cdb762d02d0bf37c9e592
sha256Value (base64): 16j7swfXgJRpypq8sAguT41WUeRtPNt2LQLQvzfJ5ZI=
sha256Base64 decoded to a byte array:
sha256Value (hex) length: 32 data: d7a8fbb307d7809469ca9abcb0082e4f8d5651e46d3cdb762d02d0bf37c9e592
sha256HexString converted to a byte array:
sha256Value (hex) length: 32 data: d7a8fbb307d7809469ca9abcb0082e4f8d5651e46d3cdb762d02d0bf37c9e592
Last update: Oct. 18th 2021
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