Importing a private key from a string using Crypto++

Question

So first I create a signing object like so:

CryptoPP::ECDSA<CryptoPP::ECP, CryptoPP::SHA256>::Signer signer;

I generate them like so:

CryptoPP::AutoSeededRandomPool prng; //Create a random number
signer.AccessKey().Initialize(prng, CryptoPP::ASN1::secp256r1());

I also validate the generated keys to check everything is fine:

signer.AccessKey().Validate(prng, 3))

These are then exported to a string:

std::string key;
CryptoPP::StringSink pss(key);
signer.AccessKey().Save(pss);

However when it comes to loading these keys back up:

CryptoPP::StringSink ss(key);
signer.AccessKey().Load(ss);

I receive and exception:

BER decode error

Just to note the signing object is blank upon attempting to load could this be it?

I'm not sure what I'm doing wrong I believe it's the method for loading the key back into the Access key and I should be importing the key to the StringSink differently but I'm not sure. Please could I have some help trying to load my keys.

Answer 1

This is correct:

 std::string p_key; CryptoPP::StringSink pss(p_key); signer.AccessKey().Save(pss); 

This looks like the problem assuming p_key and key are the same:

 CryptoPP::StringSink ss(key); signer.AccessKey().Load(ss); 

Use as StringSource when loading, not a StringSink :

CryptoPP::StringSource ss(key);
signer.AccessKey().Load(ss);

All sources and sinks are interchangeable. You can use a FileSource instead of a StringSource ; and a FileSink instead of a StringSink . But you can't replace a source with a sink (or vice versa).

StringSource and StringSink are part of pipelines in Crypto++. Pipelines and Keys and Formats from the Crypto++ wiki may be useful for you. But the code you showed is clean (other than the typo) so you may not need them.