crypto/tls: X509KeyPair cannot parse OpenSSL generated ECDSA keys

[chandra-ghub]

Please answer these questions before submitting your issue. Thanks!

I am trying to get go's standard tls package accept my openssl generated keys (Prime 256 curve ECDSA). Generated key and cert using OpenSSL -

# openssl ecparam -name prime256v1 -genkey -noout -out priv.pem -param_enc explicit
# openssl req -new -x509 -key priv.pem -out EC_server.pem -days 365

What version of Go are you using (go version)?

Tested with 1.9 and on play.golang.org too.
https://play.golang.org/p/V9GzXsn1zoG (copied the function X509KeyPair() to be able to debug)
https://play.golang.org/p/22G1XNbU8at (direct call to the library)

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

MACOS High Sierra

What did you do?

here you go -
https://play.golang.org/p/V9GzXsn1zoG with the library copied to debug the error
https://play.golang.org/p/22G1XNbU8at (without go's library code)

What did you expect to see?

A &tls.Certificate{} to have returned.

What did you see instead?

failed to parse private key error from private function parsePrivateKey() in tls.go library.

[odeke-em]

Thank for reporting this issue @chandra-ghub.

Seems like the certificate centric version of this bug is #21502, but am not sure.

I'll tag some crypto folks @agl @titanous @FiloSottile

[agl]

Drop this: -param_enc explicit

It causes OpenSSL to encode P-256 as if it were a random, arbitrary curve rather than specifying P-256 itself. The default (named_curve) is correct.

(For more details, see the OpenSSL documentation.)

[FiloSottile]

As #21502 (comment) says, -param_enc explicit is not legal for TLS certificates anyway.

I looked into making the error message more useful like in #21502 (which is indeed the same issue but with certificates) but parsePrivateKey does trial decryption of 3 formats, so we would have to guess at which is an error and which is a mismatch. I don't love that.

What we can do is move certificate parsing, which has more useful error messages, above private key parsing in X509KeyPair. I'll CL that.

[gopherbot]

Change https://golang.org/cl/90435 mentions this issue: crypto/tls: parse certificate first in X509KeyPair to get better errors

[chandra-ghub]

thanks @agl and @FiloSottile for your time. Can confirm that dropping -param_enc explicit from openssl's flags does the trick - https://play.golang.org/p/MS_FQ8cqqA8

Appreciate your acute diligence on the error messages, makes life so much easier for tls users going forward.