How to create PrivateKey by importing pem private key?

[Kejiasir]

For example, a private key string of this form：

-----BEGIN PRIVATE KEY-----
MIGTAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBHkwdwIBAQQgeeKPvGwZ92ghbN4+
bReH21oDBQnD1f0/HOs8usdsdSDuouioi77DSY9sdsa9dya89d8s/aDrJxITXeXo
/QFWM+SKDJLdfsfw4A546Jsdf/ipgevqznDVKTDJxoOK6DliXS20GQjZZ9T6xx3D
ZqoY65zp
-----END PRIVATE KEY-----

[csjones]

Hey @Kejiasir 👋

Importing a pem private key isn't supported yet. Do you have a specific use case? I can investigate your use case, check out how Apple supports pem, and see about bringing the feature into this package.

[Kejiasir]

Hello, @csjones ，thank you for your reply, CryptoKit has a constructor to create a PrivateKey from a pem private key, but it only supports iOS 14 or above. I think it would be great if secp256k1.swift could support importing pem to create a PrivateKey.

CryptoKit example:

if #available(iOS 14.0, *) {
        let prikey = """
            -----BEGIN PRIVATE KEY-----
            MIGTAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBHkwdwIBAQQgeeKPvGwZ92ghbN4+
            bReH21oDBQnD1f0/HOs8usdsdSDuouioi77DSY9sdsa9dya89d8s/aDrJxITXeXo
            /QFWM+SKDJLdfsfw4A546Jsdf/ipgevqznDVKTDJxoOK6DliXS20GQjZZ9T6xx3D
            ZqoY65zp
            -----END PRIVATE KEY-----
            """
        
        let message = "Test signature message".data(using: .utf8)!
        let privateKey = try? P256.Signing.PrivateKey(pemRepresentation: prikey)
        
        guard let signature = try? privateKey?.signature(for: message) else { return }
        
        let signDataBase64String = signature.derRepresentation.base64EncodedString()
        print("CryptoKit: \(signDataBase64String)")
        
        let publicKey = privateKey?.publicKey
        let isValidSignature = publicKey?.isValidSignature(signature, for: message)
        print("CryptoKit: \(isValidSignature)")
}

[csjones]

Hey @Kejiasir - want to double check, are you sure you need seccp256k1? I ask because CryptoKit uses seccp256r1 and it wouldn't matter what iOS version this package supports.

[Kejiasir]

Hey @csjones Yes, I need to use the ecdsa signature algorithm to generate signatures in versions below iOS14. Since I need to create a PrivateKey by importing a pem key, so far, I have not found a more suitable third-party library to achieve it.

[csjones]

Hey @Kejiasir how are you generating these pem keys?

[Kejiasir]

Hey @csjones This is Apple's official document, and I followed this guideline. Generate keys for in-app purchases

[csjones]

Hey @Kejiasir I think this package isn't what you need based on those Apple instructions and none of the documentation mentions secp256k1. Are you aware of this Swift package? It has support prior to iOS 13.

I am still planning to add PEM key support but I don't have a good test case for basing the implementation on.