From: Brian Candler <b.candler@...>
Date: 2010-09-01T20:42:45+09:00
Subject: Re: rsa sign and verify with openssl on windows

Here are some tests on ubuntu Lucid with ruby 1.8.7

$ openssl genrsa -out priv.pem 1024
Generating RSA private key, 1024 bit long modulus
....++++++
...................++++++
e is 65537 (0x10001)

$ openssl rsa -in priv.pem -out pub.pem -pubout
writing RSA key

$ irb --simple-prompt
>> require 'openssl'
=> true
>> private_key = OpenSSL::PKey::RSA.new(File.read('priv.pem')); nil
=> nil
>> File.open("pub2.pem","w") { |f| f.write private_key.public_key }
=> 251

$ cat pub.pem
-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCx5oz9tweJf4OZaM3y/0JRUeS3
Ctyy7zuPmrf2D/EK6GO4a+8OIG/Q++XskSIrqFUXAMjVDfM4zrGAwdzVRaKBo5an
2YskZFfT5YizOxyzyxjQ7+Z7kgNH7O7KEXCXOdSa8Bg3qQp40ChVI4kpdWTYlmS5
YY7lWqRLTAYYdVkVAQIDAQAB
-----END PUBLIC KEY-----

brian@zino:~$ cat pub2.pem
-----BEGIN RSA PUBLIC KEY-----
MIGJAoGBALHmjP23B4l/g5lozfL/QlFR5LcK3LLvO4+at/YP8QroY7hr7w4gb9D7
5eyRIiuoVRcAyNUN8zjOsYDB3NVFooGjlqfZiyRkV9PliLM7HLPLGNDv5nuSA0fs
7soRcJc51JrwGDepCnjQKFUjiSl1ZNiWZLlhjuVapEtMBhh1WRUBAgMBAAE=
-----END RSA PUBLIC KEY-----

Now, I see that openssl is happy with pub.pem:

$ openssl rsa -in pub.pem -pubin -noout -text

but fails to read pub2.pem (even if you change "RSA PUBLIC KEY" to 
"PUBLIC KEY")
$ openssl rsa -in pub2.pem -pubin -noout -text

Ruby can read it back though (although interestingly, ruby 1.8.6 under 
Ubuntu Hardy cannot)

>> public_key = OpenSSL::PKey::RSA.new(File.read("pub2.pem"))
=> -----BEGIN RSA PUBLIC KEY-----
MIGJAoGBALHmjP23B4l/g5lozfL/QlFR5LcK3LLvO4+at/YP8QroY7hr7w4gb9D7
5eyRIiuoVRcAyNUN8zjOsYDB3NVFooGjlqfZiyRkV9PliLM7HLPLGNDv5nuSA0fs
7soRcJc51JrwGDepCnjQKFUjiSl1ZNiWZLlhjuVapEtMBhh1WRUBAgMBAAE=
-----END RSA PUBLIC KEY-----

But I think this is probably a side-issue of outputting public keys.

The real question is, what algorithm are you trying to implement in 
ruby? Are you trying to do something along the lines of "openssl rsautl 
-sign" ? In that case, you should use the OpenSSL API for that, as it 
deals with all the padding correctly.

>> pk = OpenSSL::PKey::RSA.new(File.read("priv.pem"))
...
>> File.open("enc1.dat","wb") { |f| f.write pk.sign("sha1", "hello world") }
=> 128

This file is quite happily read by openssl command line:

$ openssl rsautl -in enc1.dat -verify -inkey priv.pem -raw -hexdump
0000 - 00 01 ff ff ff ff ff ff-ff ff ff ff ff ff ff ff 
................
0010 - ff ff ff ff ff ff ff ff-ff ff ff ff ff ff ff ff 
................
0020 - ff ff ff ff ff ff ff ff-ff ff ff ff ff ff ff ff 
................
0030 - ff ff ff ff ff ff ff ff-ff ff ff ff ff ff ff ff 
................
0040 - ff ff ff ff ff ff ff ff-ff ff ff ff ff ff ff ff 
................
0050 - ff ff ff ff ff ff ff ff-ff ff ff ff 00 30 21 30 
.............0!0
0060 - 09 06 05 2b 0e 03 02 1a-05 00 04 14 2a ae 6c 35 
...+........*.l5
0070 - c9 4f cf b4 15 db e9 5f-40 8b 9c e9 1e e8 46 ed 
.O....._@.....F.

And you can see that it includes the expected digest in the last 20 
bytes:

$ echo -n "hello world" | openssl dgst -sha1 -hex
2aae6c35c94fcfb415dbe95f408b9ce91ee846ed
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