CODEWITHSUNDEEP
utf-8character-encodingbase64decodeutf-16
Sahad Nk
Sahad Nk

Reputation: 79

Decoded value of base64 string when re-encoded(to base64) gives different output

I'm really confused about something here. When I decode the following base64 string 

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

The output is:

FZ!?A,�U"WwwwwwwwwXHTransactional: Aaaaaaaa Gggggg ?XU恍[email protected] QD駴tps://www.abcdefgh.com/endpoint--name?id=62FYPW&valu=2ffg92080f22c50c6grsd349frtyuio9&utm_campaign=Transactional%3A%20Password%20Reset&utm_source=SparkPost&utm_medium=email&utm_term=Transactional%3A%20Pppp%20Mainn&referer=62FYPWGQ{"email_user":"14785243699632.288207406700815289974144","binding":"notifications"}

But when I try to encode the same output value back to base64 it gives me:

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

What's happening here?

If decode(base64_A) is giving me x, and encode(x) gives me base64_B, how can I generate base64_A from x or base64_B?

Upvotes: 2

Views: 2113

Answers (1)

Remy Lebeau
Remy Lebeau

Reputation: 597941

The decoded text you have shown contains non-ASCII characters in it. Base64 encodes binary data only, so you have to take character encodings into account when encoding/decoding text.

When encoding base64, a character string has to be charset-encoded to bytes first, such as with UTF-8, and then those bytes can be encoded with base64.

When decoding base64, the result is bytes, which can then be charset-decoded to a character string.

If you use the wrong charset, you will get incorrect results.

Upvotes: 1

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