Ruby OpenSSL RSA decryption failing due to padding check failed

Question

I'm trying to replicate the following python code in ruby. The python code works fine, the ruby code fails due to "padding check failed". I can encrypt a string and decrypt it with the private key in Ruby, but the encrypted data I need to work with is being retrieved from elsewhere. I'm unsure of the library and even language used to encrypt it, but the Python code works.

Working Python code:

def decrypt_secret(encrypted_base64, private_key):
  key = RSA.importKey(open(private_key, "r").read())
  pkey = PKCS1_OAEP.new(key, hashAlgo=SHA256)
  encrypted_blob = base64.urlsafe_b64decode(encrypted_base64)
  decrypted_string = pkey.decrypt(encrypted_blob)
  return decrypted_string

Ruby Code fails "padding check failed"

def decrypt_secret(encrypted_base64, private_key)
  key = File.read(private_key)
  pkey = OpenSSL::PKey::RSA.new(key)
  encrypted_blob = Base64.urlsafe_decode64(encrypted_base64)
  decrypted_string = pkey.private_decrypt(encrypted_blob, OpenSSL::PKey::RSA::PKCS1_OAEP_PADDING)
  return decrypted_string
end

Andy Fraley · Accepted Answer · 2017-03-31 13:39:51Z

4

I found the needed functions contained in the JOSE gem to support SHA256 OAEP. The following code does the job:

require 'jose'
def decrypt_secret(encrypted_base64, private_key)
  key = File.read(private_key)
  pkey = OpenSSL::PKey::RSA.new(key)
  encrypted_blob = Base64.urlsafe_decode64(encrypted_base64)
  decrypted_string = JOSE::JWA::PKCS1::rsaes_oaep_decrypt(OpenSSL::Digest::SHA256, encrypted_blob, pkey)
  return decrypted_string
end

answered Mar 31, 2017 at 13:39

Andy Fraley

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Comments

Artjom B. · Accepted Answer · 2017-03-30 18:34:39Z

1

It doesn't look like Ruby's OpenSSL wrapper exposes the option to change the hash function for OAEP. You would need to change the Python code to use SHA-1 (default):

pkey = PKCS1_OAEP.new(key)

answered Mar 30, 2017 at 18:34

Artjom B.

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