TIL: Asymmetric Cryptography in Go

I’ve been implementing a feature at work that involves asymmetric cryptography. It has been a pretty fun exercise in stitching together Go APIs while reading about best practices.

Here’s a few things I’ve learned over the last couple of days:

• Go’s cryptography isn’t FIPS compliant.

• Go has an implementation of ECDSA (Elliptic Curve Digital Signature Algorithm), but it doesn’t have any elliptic curve asymmetric encryption algorithms.

  • The best asymmetric algorithm that Go has is RSA

• Go has an implementation of PEM (Privacy Enhanced Mail) data encoding which can be used to encode public/private in a familiar format. You’ve probably seen this format with SSH keys:

  -----BEGIN PUBLIC KEY-----
  MIIEpAIBAAKCAQEAuOuUOwNRMbqc0jMEVTOyKuVUu0bk0zD5iwIggBHpDhV58DSJ
  SK7OFIFHVMy6FKg2B3Y50srfVJ45OE9Vsb9hfErUNA/PB5meHGEI+yPKeni4GAfy
  <and so on>
  -----END PUBLIC KEY-----
  

• The legacy PEM format has support for plaintext headers like so:

  -----BEGIN PUBLIC KEY-----
  Data: Some value I don't mind being plaintext
  
  MIIEpAIBAAKCAQEAuOuUOwNRMbqc0jMEVTOyKuVUu0bk0zD5iwIggBHpDhV58DSJ
  SK7OFIFHVMy6FKg2B3Y50srfVJ45OE9Vsb9hfErUNA/PB5meHGEI+yPKeni4GAfy
  <and so on>
  -----END PUBLIC KEY-----
  

  • The newer RFC eplicitly doesn’t support headers, though:

    Unlike legacy PEM encoding RFC1421, OpenPGP ASCII armor, and the OpenSSH key file format, textual encoding does not define or permit headers to be encoded alongside the data.

• Go’s APIs for encrypting, decrypting, signing, and verifying data are quite pleasant to use!

  • The Go examples illustrate this quite well.

• When signing data, Go will first have you run that data through a hash algorithm (e.g. SHA256). This actually makes quite a bit of sense, and it helps me better understand why secure hashing is important for cryptography.

• OWASP (Open Worldwide Application Security Project) has a great section on encryption algorithms which can help guide those less familiar with the specifics of encryption.

• There are a few algorithms for signing and encryption data with RSA. Go implements PKCS1v15 and OAEP for encryption, and PKCS1v15 and PSS for signing.

  • This Stack Exchange answer goes into the details of these algorithms.

While I’m generally not a huge fan of Go, I do think the standard library has some nice packages, and the encryption library is definitely one of them.