Wednesday, 31 May 2017

Slide - SAML, Variants, Functors, Monads and Exceptions

A presentation I gave at work (SAP Concur) on SAML, using variants and exception handling in Clojure, functors, applicative functors and monads in Haskell and how Maybe and Either monads short circuits during exception and such. Removed some internal code and links.


The variant C code can be downloaded from Github.
Download this slide from Github.

Friday, 12 May 2017

BlackBerry Passport MicroSDXC Card Support

BlackBerry Passport supports microSD cards upto 128GB. microSDXC cards can also be used with it. However, BlackBerry 10 recognises only FAT formatted external partitions and these cards comes mostly with ExFAT. So the device will show that the media card is not supported and is downloading drivers, but it will fail with an error. To fix this, erase the card and choose FAT as the partition format. Then the OS will recognise the microSDXC card.

Monday, 8 May 2017

Get RSA PublicKey from XML Key Format

Here is a script (prototype) in Groovy to get RSA PublicKey from XML public key. You might encounter such XML keys, say during .NET interop.
import javax.xml.parsers.DocumentBuilder
import javax.xml.parsers.DocumentBuilderFactory
import org.w3c.dom.Document
import java.nio.charset.StandardCharsets
import java.security.spec.RSAPublicKeySpec
import java.security.KeyFactory
import java.security.PublicKey

def rsaPubXML = "ANxn+vSe8nIdRSy0gHkGoJQnUIIJ3WfOV7hsSk9An9LRafuZXYUMB6H5RxtWFm72f7nPKlg2N5kpqk+oEuhPx4IrnXIqnN5vwu4Sbc/w8rjE3XxcGsgXUams3wgiBJ0r1/lLCd6a61xRGtj4+Vae+Ps3mz/TdGUkDf80dVek9b9VAQAB"
def docBuilderFactory = DocumentBuilderFactory.newInstance()
def docBuilder = docBuilderFactory.newDocumentBuilder()

def b64Decode(enc) {
    Base64.getDecoder().decode(enc)
}

Document xmlDoc = docBuilder.parse(new ByteArrayInputStream(rsaPubXML.getBytes(StandardCharsets.UTF_8)))

def modulus = xmlDoc.getElementsByTagName("Modulus").item(0).textContent
def exponent = xmlDoc.getElementsByTagName("Exponent").item(0).textContent
println "modulus: ${modulus}\nexponent: ${exponent}"

RSAPublicKeySpec keySpec = new RSAPublicKeySpec(new BigInteger(b64Decode(modulus)), new BigInteger(b64Decode(exponent)));
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
PublicKey key = keyFactory.generatePublic(keySpec);

println "key: ${key}"
This gives the following output.
modulus: ANxn+vSe8nIdRSy0gHkGoJQnUIIJ3WfOV7hsSk9An9LRafuZXYUMB6H5RxtWFm72f7nPKlg2N5kpqk+oEuhPx4IrnXIqnN5vwu4Sbc/w8rjE3XxcGsgXUams3wgiBJ0r1/lLCd6a61xRGtj4+Vae+Ps3mz/TdGUkDf80dVek9b9V
exponent: AQAB
key: Sun RSA public key, 1024 bits
  modulus: 154774478177095248394968828543369801032226937226535865231262824893513573019304152154974259955740337204606655133945162319470662684517274530901497375379716962851415879364453962123395223899051919634994929603613704222239797911292193776910691509004328773391280872757318122152217457361921195935350223751896771182421
  public exponent: 65537
Note that the modulus must be a positive integer. If you are working with other JVM languages and are getting a negative integer value, specify the signum as 1 in the BigInteger(1, b64Decode(modulus)) function call. The exponent must always be 65537 as of now because that is the largest Fermat's Prime known today.