Feature #12354: PKey::EC Can't output public key pem when private key exists

• Status: Assigned
• Priority: Normal
• Assignee: rhenium (Kazuki Yamaguchi)
• Target version: -

[armour (Armour Comms)]

Steps to reproduce:

Create EC key:

key = OpenSSL::PKey::EC.new("prime256v1")
key.generate_key

Try and output in pem format

key.to_pem #Outputs private key pem
key.public_key.to_pem #Error

In order to output a public key pem, a new key object must be created with no private key:

key_pub = OpenSSL::PKey::EC.new(key.group)
key_pub.public_key = key.public_key

Output pem

key_pub.to_pem #Success!

From viewing the source, http://rxr.whitequark.org/mri/source/ext/openssl/ossl_pkey_ec.c#466 it seems that if the key is private there is no way to output a public key for that key object

[hsbt (Hiroshi SHIBATA)]

• Assignee set to rhenium (Kazuki Yamaguchi)
• Status changed from Open to Assigned
• Description updated (diff)

[jeremyevans0 (Jeremy Evans)]

• Backport deleted (2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN)
• ruby -v deleted (ruby 2.2.4p230 (2015-12-16 revision 53155) [x86_64-linux])
• Tracker changed from Bug to Feature

The following is a way to generate a PEM for a OpenSSL::PKey::EC with both a private and a public key without allocating a new OpenSSL::PKey::EC:

pk = key.private_key
key.private_key = nil
key.to_pem
key.private_key = key

I agree that this approach is suboptimal, and it may be worthwhile to add a method for this, or a keyword argument to to_pem. However, that is a request for a new feature, not a bug fix.

I checked and OpenSSL::PKey::RSA doesn't have the same issue because OpenSSL::PKey::RSA#public_key returns OpenSSL::PKey::RSA (OpenSSL::PKey::EC returns OpenSSL::PKey::EC::Point). However, it still requires allocating a new OpenSSL::PKey::RSA object.