Computer Security Algorithms

Problems related to computer security. Algorithms written in Python. Follow the Tutorial

Main topics (Tags)

• RSA: RSA stands for Rivest-Shamir-Adleman. Is a widely used public-key cryptosystem "based on the practical difficulty of factoring the product of two large prime numbers" (RSA cryptosystem)

• PublicKey-Crypto:

• Hashing: A hash function maps data of arbitrary size to data of fixed size. An ideal hash function maps randomly, avoid colissions and is impossible to invert.

• Symmetric-Crypto:

• Classical-Crypto:

• Passwords:

• AES:

• Tutorial:

• Bitcoin:

• PGP: PGP stands for Pretty Good Privacy. Is a program used to facilitate encrypt and decrypt your mail. PGP "has proven itself quite capable of resisting even the most sophisticated forms of analysis" (PGP faqs)

• ECC:

• Factoring:

• OpenSSL:

• PRNG:

Solved Problems

• Hello PGP Use PGP programatically. Recover the message encrypted with a single English word.

• Hello Bitcoin Do you know how bitcoin addresses are constructed?

• Hello OpenSSL Can you read and use an OpenSSL RSA key?

• AES-CTR with Nonce Reuse Can you exploit a reused nonce?

• Affine Cipher Can you brute force this classical cipher?

• Double Strength Affine A slight security upgrade, is it enought?

• Ps and Qs RSA keys generated with one critical weakness

• Insufficient Key Size Are you running on all 8 cores? This small key is factorable on a PC with an efficient implementation

• Elliptic Curve Private Key Recovery Given the public parameters of an elliptic curve, recover the poorly chosen private key

• Håstad's Broadcast Attack RSA with a small exponent is fast to compute but it has a serious weakness

• Monoalphabetic Cipher Monoalphabetic ciphers leak information. Can you recover it?

• Playfair This bigram cipher is a bit trickier...

• Factoring RSA With CRT Optimization Recover a RSA private key when an optimization goes wrong

• Rainbow Table Hash Chain Can you use a rainbow table to recover a password?

• ECDSA Nonce Recovery Nonce reuse leading to private key recovery, this time with elliptic curves

• Intro to Hashing Hashing is a vital concept in cryptography

• Intro to PGP Can you use PGP programatically?

• Intro to RSA Learn the basics of a common public key cryptosystem

• CBC Padding Attack CBC is one of the best modes of operation for block ciphers, but even leaking a tiny amount of information is enough to completely undermine its security

• CCA on Textbook RSA Turns out padding is important

• Fast Hashing Passwords Cryptographic hash functions shouldn't be used to hash passwords directly

• Salt Alone Won't Save You Salting password hashes is important, but not enough on it's own

• Cut and Paste Attack On AES-ECB Create a valid ciphertext without knowledge of the key using some copypaste

• Insecure PRNG Using a PRNG that isn't proven to be cryptographically secure is a recipe for disaster

• Bad Entropy It's easy to generate bad symmetric keys

• Caesar Should probably stick to the salad

Unsolved Problems

• Bleichenbacher's CCA2 on RSA 14

• CRIMEs against TLS 20

• CBC Padding Attack 22

• Breaking PDF Passwords 29

• Backdoored PRNG 31

• Vigenère 33

• Rail Fence 34

• Vigenère + Rail Fence 35

• Not So Safe Primes 37