How do I convert an XML RSA key to a PEM file?

I have two XML files, structured as follows:

My Key

<RSAKeyValue>
  <Modulus> ... </Modulus>
  <Exponent> ... </Exponent>
  <P> ... </P>
  <Q> ... </Q>
  <DP> ... </DP>
  <DQ> ... </DQ>
  <InverseQ> ... </InverseQ>
  <D> ... </D>
</RSAKeyValue>

A Public Key

<RSAKeyValue>
   <Modulus> ... </Modulus>
   <Exponent> ... </Exponent>
</RSAKeyValue>

I am using the xmlseclibs library by Robert Richards which requi开发者_如何学Cres a .PEM representation of the key in order to encrypt and decrypt things.

As an encryption novice, I'm not sure where to begin, and a cursory Google search did not reveal anything particularly obvious...

Thanks!

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I have found a Java utility that can do it.

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For those who want the resulting PEM to be readable by BouncyCastle:

1. use XMLSec2PEM tool to get a pem file
2. convert pem to pkcs8 and back (!)

The final solution I am happy with:

1. java XMLSec2PEM my.xml > my.pem
2. edit my.pem manually a bit
3. org.bouncycastle.openssl.PEMReader.readObject() returns null :-(
4. openssl pkcs8 -topk8 -inform pem -in my.pem -outform pem -nocrypt -out my.pkcs8
5. openssl pkcs8 -inform pem -nocrypt -in my.pkcs8 -out my.pkcs8.pem
6. now my.pkcs8.pem is readable with the PEMReader

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my solution in python works like this:

1. extract modulus and exponent from xml

   xml = etree.fromstring(key_bin)
   modulus = xml.find('Modulus').text
   exponent = xml.find('Exponent').text
   

2. decode them in base64 and iterate the result to save it as a character string of length 2:

   mod_b64 = b64decode(modulus.encode())
   exp_b64 = b64decode(exponent.encode())
   exp = ''.join(['{:02x}'.format(x) for x in exp_b64])
   mod = ''.join(['{:02x}'.format(x) for x in mod_b64]) 
   

3. Convert the hexadecimal string to integer and generate the rsa public key with the rsa library:

   exp_num = int(exp, 16)
   mod_num = int(mod, 16)
   rsa_key = rsa.PublicKey(mod_num, exp_num)
   

4. Finally any text can be encrypted:

   msg_cryp = rsa.encrypt(msg.encode('ascii'), rsa_key)
   msg_cryp_str = b64encode(msg_cryp).decode('ascii') 
   

I did this development to consume a web service which requires that an encrypted password be sent from a public key in XML format. In this way I managed to encrypt the password and consume the web service without problems.

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I was searching for hours for exactly the same problem. This Java tool did the job :)

But the link has changed, it is now available from here

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Since xmlseclibs is PHP it seems like another PHP solution might be desirable. Here's how:

<?php
include('Crypt/RSA.php');

$rsa = new Crypt_RSA();
$rsa->loadKey('<RSAKeyValue>
  <Modulus> ... </Modulus>
  <Exponent> ... </Exponent>
  <P> ... </P>
  <Q> ... </Q>
  <DP> ... </DP>
  <DQ> ... </DQ>
  <InverseQ> ... </InverseQ>
  <D> ... </D>
</RSAKeyValue>');

$privatekey = $rsa->getPrivateKey();
$publickey = $rsa->getPublicKey();
?>

phpseclib has built in support for XML keys, PuTTY keys and PKCS1 keys. It'll auto detect the format and load it and getPrivateKey / getPublicKey will output PKCS1 formatted keys by default if no parameters are provided. More info:

http://phpseclib.sourceforge.net/rsa/examples.html#convert

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Here is a ruby version script to convert RSA to pem, vice versa.

1. Make sure Ruby has been installed.

2. start irb in your terminal

   > irb
   

3. Paste the following code to the irb console.

   require 'openssl'
   require 'base64'
   require 'rexml/document'
   
   class PKeyRSAConverter
     def initialize(from_pem:nil, from_xml:nil)
       @from_pem = from_pem
       @from_xml = from_xml
     end
   
     def to_xml
       xml  = '<RSAKeyValue>'
       xml += "<Modulus>#{xml_base64(xml_pkey.n)}</Modulus>"
       xml += "<Exponent>#{xml_base64(xml_pkey.e)}</Exponent>"
       xml += '</RSAKeyValue>'
       xml
     end
   
     def to_pem
       pem_key.to_pem
     end
   
     private
   
     def pem_key
       exponent = xml_find_exponent.to_s
       modulus = xml_find_modulus.to_s
       key = OpenSSL::PKey::RSA.new
       key.set_key(pem_base64(modulus), pem_base64(exponent), nil)
       key
     end
   
     def xml_find_modulus
       REXML::XPath.match(xml_document.root, "//RSAKeyValue/Modulus/text()")[0]
     end
   
     def xml_find_exponent
       REXML::XPath.match(xml_document.root, "//RSAKeyValue/Exponent/text()")[0]
     end
   
     def xml_document
       @xml_document ||= REXML::Document.new(@from_xml.to_s)
     end
   
     def pem_base64(string)
       Base64.urlsafe_decode64(string).bytes.inject(0){|a,e| (a << 8)| e }
     end
   
     def xml_pkey
       @xml_pkey ||= OpenSSL::PKey::RSA.new(@from_pem)
     end
   
     def xml_base64(int)
       Base64.encode64([int.to_s(16).downcase].pack('H*')).split("\n").join
     end
   end
   

4. pem -> xml

   Here is an example to convert PEM to xml

   rsa_pem="-----BEGIN PUBLIC KEY-----\nMFwwDQYJKoZIhvcNAQEBBQADSwAwSAJBAJYOlB8N/EdJL9nqEsRNF+No/9QkmPaX\n/xxpPleZTTNgakTkUlmyZPud8eEGsaX7nLgoVF39zTrXeg4hIeaWsAsCAwEAAQ==\n-----END     PUBLIC KEY-----\n"
   
   puts 'Convert PEM to XML'
   to_xml = PKeyRSAConverter.new(from_pem: rsa_pem).to_xml
   puts to_xml == rsa_xml
   

5. xml -> pem

   Here is an example to convert xml to PEM

   rsa_xml="<RSAKeyValue><Modulus>lg6UHw38R0kv2eoSxE0X42j/1CSY9pf/HGk+V5lNM2BqRORSWbJk+53x4QaxpfucuChUXf3NOtd6DiEh5pawCw==</Modulus><Exponent>AQAB</Exponent></RSAKeyValue>"
   
   puts 'Convert XML to PEM'
   to_pem = PKeyRSAConverter.new(from_xml: rsa_xml).to_pem
   puts rsa_pem == to_pem
   

Reference

1. Github Gist: anicet/pkey_rsa_converter.rb

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Found this useful online tool RSA Key Converter, which supports

• XML -> PEM
• PEM -> XML