Does this library support interop with pycrypto?

[ColtonIdle]

Just getting started in this field but for my job i have to provide interop (both ways) with a python library.

https://pycryptodome.readthedocs.io/en/latest/src/signature/dsa.html

so basically im trying to replicate these two functions in kotlin

A sender can use a private key (loaded from a file) to sign a message:

from Crypto.Hash import SHA256
from Crypto.PublicKey import ECC
from Crypto.Signature import DSS

message = b'I give my permission to order #4355'
key = ECC.import_key(open('privkey.der').read())
h = SHA256.new(message)
signer = DSS.new(key, 'fips-186-3')
signature = signer.sign(h)

and

The receiver can use the matching public key to verify authenticity of the received message:

from Crypto.Hash import SHA256
from Crypto.PublicKey import ECC
from Crypto.Signature import DSS

key = ECC.import_key(open('pubkey.der').read())
h = SHA256.new(received_message)
verifier = DSS.new(key, 'fips-186-3')
try:
    verifier.verify(h, signature)
    print("The message is authentic.")
except ValueError:
    print("The message is not authentic.")

but i dont see any mention of fips-186-3 in this library/sample code so im not sure if that fips-186-3 is just a standard and i dont need to actually declare that in my kotlin code anywhere?

[whyoleg]

Hey! Yeah, there is no need to provide fips-186-3, this is the default behaviour now. So everything should work fine.
The main difference with this python library is that you don't need to hash data yourself, but it will be done under the hood.

So to mimic your code here, it will be something like this:

val ecdsa = CryptographyProvider.Default.get(ECDSA)
val signature =
    ecdsa
        .privateKeyDecoder(EC.Curve.P521)
        .decodeFrom(EC.PrivateKey.Format.DER, TODO("read bytes from 'privkey.der'"))
        .signatureGenerator(SHA256, ECDSA.SignatureFormat.RAW) // python lib used RAW format by default
        .generateSignature("I give my permission to order #4355".encodeToByteArray())

val isValid =
    ecdsa
        .publicKeyDecoder(EC.Curve.P521)
        .decodeFrom(EC.PublicKey.Format.DER, TODO("read bytes from 'pubkey.der'"))
        .signatureVerifier(SHA256, ECDSA.SignatureFormat.RAW)
        .verifySignature("I give my permission to order #4355".encodeToByteArray(), signature)
check(isValid) { "Signature is invalid" }

The only thing that is not supported is automatic decoding of curves - you need to provide it explicitly.

Hope this helps!

[ColtonIdle]

Oh heck yeah! This is insanely helpful as I've been going insane trying to match that same logic.

I noticed in the docs that this might not be supported on iOS. Is that right?

I was able to get it working with CryptoKit/Security so it's not the biggest deal. but would be nice to have a single interface for it.

FWIW, this was my code that worked (to decode at least. haven't done encoding/signing)

let publicKey = try! P256.Signing.PublicKey(pemRepresentation: pemString)

let signature = try! P256.Signing.ECDSASignature(rawRepresentation: Data(hex: "hex representation here")!)

let isValid = publicKey.isValidSignature(signature, for: "put the bytes here".data(using: .utf8)!)
print("Is valid: (isValid)")

[whyoleg]

It's supported only with openssl provider on iOS in 0.3.1.
But in the next release, there will be support also in apple provider, which is also available for iOS.

[ColtonIdle]

Interesting! This is all still new to me. so it seems like I can use this with iOS! Awesome. I just need to use the openssl provider on apple as well? Hm. I'm new to kmp, let me see if I can get my dependencies looking right

maybe something like this should work

iosMain.dependencies {
    implementation("dev.whyoleg.cryptography:cryptography-provider-openssl:0.3.1")
}

androidMain.dependencies {
    implementation("dev.whyoleg.cryptography:cryptography-provider-jdk:0.3.1")
}

commonMain.dependencies {.   
implementation("dev.whyoleg.cryptography:cryptography-core:0.3.1")
}

[whyoleg]

Yes, you got it right!

here is an example: #27 (comment)

kotlin {
    sourceSets {
        commonMain.dependencies {
            implementation(project.dependencies.platform("dev.whyoleg.cryptography:cryptography-bom:0.3.1"))
            implementation("dev.whyoleg.cryptography:cryptography-core")
        }
        androidMain.dependencies {
            implementation("dev.whyoleg.cryptography:cryptography-provider-jdk")
        }
        iosMain.dependencies {
            implementation("dev.whyoleg.cryptography:cryptography-provider-openssl3-prebuilt")
            // or `apple` provider
            // implementation("dev.whyoleg.cryptography:cryptography-provider-apple")
        }
    }
}

P.S. I will definitely add this to the docs/readme in upcoming release...

[ColtonIdle]

Ah nice. That is exactly what i was looking for! updating the readme will be excellent. cheers