Request for an API to verify signatures

[sethladd]

A customer asked for "anything to help me check a payload against an RSA public key signature? (I think I want to use the sha256WithRSAEncryption algo)." and "I only need the functionality of Chrome's SignatureVerifier class[1], which uses openssl's EVPPKEY* and EVP_DigestVerify* and friends."

[sethladd]

cc @mpcomplete

[nex3]

@mpcomplete @sethladd Can one of you provide a link to the specification for the signature-verification algorithm you're referring to?

[sethladd]

I defer to @mpcomplete

[mpcomplete]

I can't find a spec, but it's part of the X509 signature block. I want to be able to verify a X509 SubjectPublicKeyInfo block using the sha256WithRSAEncryption algorithm. In other words, given a signature, key, and file generated on the command line like so:

echo "Verified text." > file.txt echo "Invalid text." > tampered.txt openssl genrsa -out privatekey.pem 2048 openssl rsa -in privatekey.pem -outform PEM -pubout -out publickey.pem openssl dgst -sha256 -sign privatekey.pem -binary -out signature.sign file.txt

I want to be able to do the equivalent to:

openssl dgst -sha256 -verify publickey.pem -signature signature.sign file.txt ; # should verify OK openssl dgst -sha256 -verify publickey.pem -signature signature.sign tampered.txt ; # should FAIL

This might just be a matter of exposing the appropriate openssl methods to dart.

Something with the functionality of Chrome's SignatureVerifier would work: https://code.google.com/p/chromium/codesearch#chromium/src/crypto/signature_verifier_openssl.cc&sq=package:chromium&type=cs .

[nex3]

It looks like sha256WithRSAEncryption() is described in RFC 5754, section 3.2, although I'm not sure how to read that.

This might just be a matter of exposing the appropriate openssl methods to dart.

Unfortunately, there's not a good way to get access to native code in Dart, at least from a package. Unless we want to put this into the core libraries somehow, someone will need to port the algorithm to Dart.

[mpcomplete]

Actually, Julien Tinnes recommended against using RSA for signing purposes. Instead, he recommends "SHA256 + ECDSA on P-256".

Equivalent openssl commands:

echo "Verified text." > file.txt echo "Invalid text." > tampered.txt openssl ecparam -genkey -name prime256v1 -out privatekey.pem openssl ec -in privatekey.pem -outform PEM -pubout -out publickey.pem

openssl dgst -sha256 -sign privatekey.pem -binary -out signature.sign file.txt

openssl dgst -sha256 -verify publickey.pem -signature signature.sign file.txt openssl dgst -sha256 -verify publickey.pem -signature signature.sign tampered.txt