(Not only) Android malware analysis

The best way to fight crypto-ransomware is to have backups. But what if you make backups once a month, but want to decrypt all of the new or modified files? Is it possible? Sometimes... Recently, I had a lot of encounters with cryptography . Additionally, this year marks the 70th anniversary of the end of the Second World War. Rather unusually, this two facts combined can help us fight ransomware. We will also learn something about different kinds of ciphers and their weaknesses. Some versions of the crypto-ransomware use streaming cipher (usually RC4) to encrypt the files found on the victim's machine. However, they make a serious mistake that would get them in trouble if they were working in the Nazi's communication department. But first, let me tell you something about the idea behind the streaming ciphers. Most symmetric streaming ciphers are using on the same idea. Based on the password provided by the user, encryption/decryption algorithm creates a keystream....

Martijn Grooten on Twitter  (with his signature sarcastic undertone) posed a weekend challenge for anyone interested in cryptography: have fun with Crystalline Cipher and show that it is fundamentally broken. Now, I've met with Martijn only once, but from that meeting I gathered that he really loves mathematics, at least as much as I do, and has a great understanding of cryptography. This whole business with Crystalline started off with the discussion on irtf.org , when the cipher author was convincing everyone that he discovered the best cipher in the world.  But to Martijn, mailing list members and me the cipher has a smell of snakeoil. Since this weekend turned out to be rather free for me, I decided to have a go at cryptoanalysis. Mind you, I'm not in any way formally trained in cryptography. I've had two one semester long cryptography courses - one from more mathematical standpoint and the other one from more technical standpoint. The most complex cryptographic ...