cryptography: add/improve resources

Author: sharmaeklavya2

cryptography.md

@@ -1,7 +1,10 @@
 # Cryptography
 
-- https://goo.gl/KFsy54
+- [YouTube - Introduction to Cryptography by Christof Paar](https://goo.gl/KFsy54)
 - https://www.coursera.org/learn/crypto
+- [Book - Introduction to Modern Cryptography, by Katz and Lindell](https://repo.zenk-security.com/Cryptographie%20.%20Algorithmes%20.%20Steganographie/Introduction%20to%20Modern%20Cryptography.pdf):
+This book emphasizes mathematical rigor (precise definitions and proofs)
+and is helpful if you're looking to build a strong theoretical foundation.
 - https://crypto.stanford.edu/~dabo/cryptobook/BonehShoup_0_4.pdf (for book lovers)
 - https://cryptopals.com/
 - http://doctrina.org/How-RSA-Works-With-Examples.html