Base 64 URL Decoding Wtih Base64Decoder?

[hc12...@gmail.com]

Hi,

I noticed that Base64URLDecoder exists but unfortunately, I am stuck with 5.6.2, which doesn't have it.

So I followed the recommendation on https://www.cryptopp.com/wiki/Base64Decoder (Changing Alphabets section):

// my code snippet

        std::string decoded_key;

        const byte ALPHABET[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";

        int lookup[256];

        CryptoPP::Base64Decoder::InitializeDecodingLookupArray(lookup, ALPHABET, 64, false);

        try

        {

                CryptoPP::Base64Decoder* pDecoder = new CryptoPP::Base64Decoder();

                pDecoder->IsolatedInitialize(CryptoPP::MakeParameters(CryptoPP::Name::DecodingLookupArray(),(const int *)lookup));

                pDecoder->Attach(new CryptoPP::StringSink(decoded_key));

                // Decode the key since it is base64url encoded

                CryptoPP::StringSource src(key, true, pDecoder);

But then I got an exception:

AlgorithmParametersBase: parameter "DecodingLookupArray" not used

Am I missing something?

Thanks in advance!

[Jeffrey Walton]

On Tuesday, April 3, 2018 at 11:46:00 PM UTC-4, hc12...@gmail.com wrote:

Hi,

I noticed that Base64URLDecoder exists but unfortunately, I am stuck with 5.6.2, which doesn't have it.

It can be available in all versions of the library. Just copy/paste it from the existing sources :)
 

So I followed the recommendation on https://www.cryptopp.com/wiki/Base64Decoder (Changing Alphabets section):

// my code snippet

        std::string decoded_key;

        const byte ALPHABET[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";

        int lookup[256];

        CryptoPP::Base64Decoder::InitializeDecodingLookupArray(lookup, ALPHABET, 64, false);

        try

        {

                CryptoPP::Base64Decoder* pDecoder = new CryptoPP::Base64Decoder();

                pDecoder->IsolatedInitialize(CryptoPP::MakeParameters(CryptoPP::Name::DecodingLookupArray(),(const int *)lookup));

                pDecoder->Attach(new CryptoPP::StringSink(decoded_key));

                // Decode the key since it is base64url encoded

                CryptoPP::StringSource src(key, true, pDecoder);

But then I got an exception:

AlgorithmParametersBase: parameter "DecodingLookupArray" not used

Not sure why you are catching the exception but...

You can add false as a thid parameter to avoid the exception:

    MakeParameters(Name::DecodingLookupArray(),(const int *)lookup), false);

I'm not sure what trouble you might encounter afterwards, like failure to change the alphabet or changing the alphabet for all decoders.

In the end, I recommend the copy/paste method to get it.

Jeff

[Henry Chan]

Yeah, I did try to set the 3rd parameter to false to suppress the exception.

Tho, I am having trouble to get the correct hashed string (I didn't paste that part of the code, which depends on the decoded string); and I wonder it has something to do with my usage of Base64Decoder, and the exception caught my attention...

Yes, I guess I will just copy and paste the class if nothing else I can find.

Thanks for your input :)

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