The document provides an introductory overview of cryptography, explaining key topics such as hashing, encryption, digital signatures, and key derivation functions. It covers various cryptographic algorithms, including symmetric ciphers like AES and hash functions like SHA-2 and Argon2, emphasizing their importance for secure data storage and transmission. The speaker, Dr. Svetlin Nakov, is a seasoned expert in the field, highlighting practical applications within the domain of cryptography.

1. Hashes, MAC, Key Derivation, Encrypting Passwords,
Symmetric Ciphers & AES, Digital Signatures & ECDSA
Cryptography for Absolute Beginners
Dr. Svetlin Nakov
Co-Founder, Chief Training & Innovation
@ Software University (SoftUni)
https://nakov.com
Software University (SoftUni) – http://softuni.org

2. Table of Contents
1. About the Speaker
2. What is Cryptography?
3. Hashes, MAC Codes and Key Derivation (KDF)
4. Encrypting Passwords: from Plaintext to Argon2
5. Symmetric Encryption and AES
6. Digital Signatures, Elliptic Curves and ECDSA
2

3.  Software engineer, trainer, entrepreneur,
PhD, author of 15+ books, blockchain expert
 3 successful tech educational initiatives (150,000+ students)
About Dr. Svetlin Nakov
3

4. Book "Practical Cryptography for Developers"
4
GitHub:
github.com/nakov/pra
ctical-cryptography-
for-developers-book
Book site:
https://cryptobook.
nakov.com

5. What is Cryptography?

6.  Cryptography provides security and protection of information
 Storing and transmitting data in a secure way
 Hashing data (message digest) and MAC codes
 Encrypting and decrypting data
 Symmetric and asymmetric schemes
 Key derivation functions (KDF)
 Key agreement schemes, digital certificates
 Digital signatures (sign / verify)
What is Cryptography?
6

7. Cryptographic Hash Functions

8. What is Cryptographic Hash Function?
8
 One-way transformation, infeasible to invert
 Extremely little chance to find a collision
Some text
Some text
Some text
Some text
Some text
Some text
Some text
20c9ad97c081d63397d
7b685a412227a40e23c
8bdc6688c6f37e97cfb
c22d2b4d1db1510d8f6
1e6a8866ad7f0e17c02
b14182d37ea7c3c8b9c
2683aeb6b733a1
Text Hash (digest)
Cryptographic
hash function

9.  SHA-2 (SHA-256, SHA-384, SHA-512)
 Secure crypto hash function, the most widely used today (RFC 4634)
 Used in Bitcoin, IPFS, many others
 SHA-3 (SHA3-256, SHA3-384, SHA3-512) / Keccak-256
 Strong cryptographic hash function, more secure than SHA-2
 Used in Ethereum blockchain and many modern apps
Modern Hashes: SHA-2, SHA3
9
SHA-256('hello') = 2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7
425e73043362938b9824
SHA3-256('hello') = 3338be694f50c5f338814986cdf0686453a888b84f4
24d792af4b9202398f392

10.  BLAKE2 (BLAKE2s – 256-bit, BLAKE2b – 512-bit)
 Secure crypto hash function, very fast
 RIPEMD-160 (160-bit crypto hash)
 Considered weak, just 160-bits, still unbroken
 Broken hash algorithms: MD5, SHA-1, MD4, SHA-0, MD2
 Git and GitHub still use SHA-1 and suffer of collision attacks
Modern Hashes: BLAKE2, RIPEMD-160
10
BLAKE2s('hello') = 19213bacc58dee6dbde3ceb9a47cbb330b3d86f8cca8
997eb00be456f140ca25
RIPEMD-160('hello') = 108f07b8382412612c048d07d13f814118445acd

11. Hashes – Demo
Play with Hash
Functions Online
http://hash-functions.online-domain-tools.com
https://www.fileformat.info/tool/hash.htm

12. HMAC and Key Derivation (KDF)
MAC, HMAC, Scrypt, Argon2

13.  HMAC = Hash-based Message Authentication Code (RFC 2104)
 HMAC(key, msg, hash_func)  hash
 Message hash mixed with a secret shared key
 Used for message integrity / authentication / key derivation
MAC Codes and HMAC
13
HMAC('key', 'hello', SHA-256) = 9307b3b915efb5171ff14d8cb55fbc
c798c6c0ef1456d66ded1a6aa723a58b7b
HMAC('key', 'hello', RIPEMD-160) =
43ab51f803a68a8b894cb32ee19e6854e9f4e468

14. HMAC – Demo
Calculate HMAC-
SHA256 Online
https://www.freeformatter.com/hmac-generator.html

15.  Encryption and digital signatures use keys (e.g. 256-bits)
 Users prefer passwords  easier to remember
 KDF functions transform passwords to keys
 Key derivation function (KDF) == function(password)  key
 Don't use SHA256(msg + key)  its is insecure
 Use PBKDF2, Scrypt, Bcrypt, Argon2
 Bcrypt, Scrypt and Argon2 are modern key-derivation functions
 Use a lot of iterations + a lot of memory  slow calculations
HMAC and Key Derivation
15

16.  Scrypt (RFC 7914) is a strong cryptographic key-derivation function
 Memory intensive, designed to prevent ASIC and FPGA attacks
 key = Scrypt(password, salt, N, r, p, derived-key-len)
 N – iterations count (affects memory and CPU usage), e.g. 16384
 r – block size (affects memory and CPU usage), e.g. 8
 p – parallelism factor (threads to run in parallel), usually 1
 Memory used = 128 * N * r * p bytes, e.g. 128 * 16384 * 8 = 16 MB
 Parameters for interactive login: N=16384, r=8, p=1 (RAM=16MB)
 Parameters for file encryption: N=1048576, r=8, p=1 (RAM=1GB)
Key Derivation Functions: Scrypt
16

17. Scrypt
Live Demo
https://gchq.github.io/CyberChef/?op=Scrypt

18.  Clear-text passwords, e.g. store the password directly in the DB
 Never do anti-pattern!
 Simple password hash, e.g. store SHA256(password) in the DB
 Highly insecure, still better than clear-text, dictionary attacks
 Salted hashed passwords, e.g. store HMAC(pass, random_salt)
 Almost secure, GPU / ASIC-crackable
 ASIC-resistant KDF password hash, e.g. Argon2(password)
 Recommended, secure (when the KDF settings are secure)
Password Encryption (Register / Login)
18

19.  Argon2 is the recommended password-hashing for apps
Encrypting Passwords: Argon2
19
hash = argon2.hash(8, 1 << 16, 4, "password");
print("Argon2 hash (random salt): " + hash);
print("Argon2 verify (correct password): " +
argon2.verify(hash, "password"));
print ("Argon2 verify (wrong password): " +
argon2.verify(hash, "wrong123"));
Argon2 hash (random salt): $argon2id$v=19$m=65536,t=8,p=4$FW2kqbP+nidwHnT3Oc
vSEg$oYlK3rXJvk0Be+od3To131Cnr8JksL39gjnbMlUCCTk
Argon2 verify (correct password): true
Argon2 verify (wrong password): false
Register
Login
Invalid Login

20. Argon2
Calculate Hash / Verify Password – Online Demo
https://argon2-generator.com

21. Symmetric Encryption
AES, Block Modes, Authenticated Encryption
encrypt
(secret key)
I am a non-
encrypted
message …
decrypt
(secret key)
I am a non-
encrypted
message …

22.  Symmetric key ciphers
 Use the same key
(or password) to encrypt
and decrypt data
 Popular symmetric algorithms
 AES, ChaCha20, Twofish, Serpent, RC5, RC6
 Broken algorithms (don't use them!)
 DES, 3DES, RC2, RC4
Symmetric Key Ciphers
22

23.  Block ciphers
 Split data on blocks (e.g. 128 bits), then encrypt each block
separately, change the internal state, encrypt the next block, …
 Stream ciphers
 Work on sequences of data (encrypt / decrypt byte by byte)
 Block ciphers can be transformed to stream ciphers
 Using block mode of operation (e.g. CBC, CTR, GCM, CFB, …)
 https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation
Symmetric Key Ciphers
23

24.  AES – Advanced Encryption Standard (Rijndael)
 Symmetric key block cipher (128-bit blocks)
 Key lengths: 128, 160, 192, 224 and 256 bits
 No significant practical attacks are known for AES
 Modern CPU hardware implements AES instructions
 This speeds-up AES and secure Internet communication
 AES is used by most Internet Web sites for the https:// content
The "AES" Cipher
24

25.  AES is a "block cipher" – encrypts block by block (e.g. 128 bits)
 Supports several modes of operation (CBC, CTR, GCM, …)
 Some modes of operation (like CBC / CTR) require initial vector (IV)
 Non-secret random salt  used to get different result each time
 Recommended modes: CTR (Counter) or GCM (Galois/Counter)
 CBC may use a padding algorithm (typically PKCS7) to help splitting
the input data into blocks of fixed block-size (e.g. 128 bits)
 May use password to key derivation function, e.g. Argon2(passwd)
 May use MAC to check the password validity, e.g. HMAC(text, key)
AES Cipher Settings
25

26. The AES Encryption Process
26
input msg random IV+
AES
key+ ciphertext
input msg
MAC
key+ MAC code
input msg key+
AES
ciphertext MAC+IV+
KDF
password key kdf-salt+

27. The AES Decryption Process
27
original msg
MAC
key+ MAC code
AES
ciphertext IV+
KDF
password key
original msg
decrypt
Decryption
MAC code
compare Encryption
MAC code
key+
kdf-salt+

28. AES-256-CTR-Argon2-HMAC – Encrypt
28
some text
{cipher=AES-256-CTR-Argon2-HMACSHA256, cipherText=a847f3b2bc59278107,
cipherIV=dd088070cf4f2f6c6560b8fa7fb43f49,
kdf=argon2, kdfSalt=90c6fcc318fd273f4f661c019b39b8ed,
mac=6c143d139d0d7b29aaa4e0dc5916908d3c27576f4856e3ef487be6eafb23b39a}
Text:
pass@123Password:
AES-256-CTR-Argon2-HMACSHA256Cipher:
Encrypted message:

29. AES
Online Demo
https://myetherwallet.com/
create-wallet

30. Asymmetric Encryption
Public Key Cryptography and ECIES

31.  Uses a pair of keys: public key + private key
 Encrypt / verify by public key
 Decrypt / sign by private key
Public Key Cryptography
31

32.  Asymmetric encryption is slow and inefficient for large data
 Hybrid encryption schemes (like ECIES and RSA-OAEP) are used
 Hybrid encryption schemes
 Asymmetric algorithm encrypts a random symmetric key
 Encrypted by the user's public key
 Decrypted by the user's private key
 Symmetric algorithm (like AES) encrypts the secret message
 Message authentication algorithm ensures message integrity
Asymmetric Encryption Schemes
32

33. Asymmetric Encryption
33

34. Asymmetric Decryption
34

35. ECIES
Online
Demo
https://asecuritysite.com/encryption/ecc3

36. Digital Signatures
ECDSA, Sign / Verify

37.  Digital signatures provide message signing / verification
 Authentication (proof that known sender have signed the message)
 Integrity (the message cannot be altered after signing)
 Non-repudiation (signer cannot deny message signing)
 Digital signatures are based on public key cryptography
 Messages are signed by someone's private key
 Signatures are verified by the corresponding public key
 May use RSA, DSA, elliptic curves (ECC) like ECDSA / EdDSA
Digital Signatures – Concepts
37

38.  Well-known public-key crypto-systems
 RSA – based on discrete logarithms
 ECC – based on elliptic curves
 ECC cryptography is considered more secure
 3072-bit RSA key ≈≈ 256-bit ECC key  ~ 128-bit security level
 Most blockchains (like Bitcoin, Ethereum and EOS) use ECC
 But be warned: ECC is not quantum-safe!
Public Key Crypto Systems
38

39. ECDSA
Online Demo
https://kjur.github.io/js
rsasign/sample/sample
-ecdsa.html

40. https://nakov.com
Cryptography for Absolute Beginners