Blockchain Cryptography for Developers (Nakov @ BlockWorld 2018, Sa...

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Blockchain Cryptography for Devs
Elliptic Curves, ECC, ECDSA,
secp256k1, Hashes, Wallets, AES,
SCrypt, HMAC, BIP39, BIP44
...

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 Software engineer, trainer, entrepreneur,
PhD, author of 12 books, blockchain expert
 3 successful tech educational i...

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 Technical advisor @ LockChain / LockTrip: https://locktrip.com
 Raised ~ 10.000 ETH in token sale (Sep-Nov 2017)
 Cu...

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 Elliptic Curve Cryptography (ECC)
 ECC Concepts, Elliptic Curves, the secp256k1 Curve
 Private Key  Public Key  Bl...

Elliptic Curve Cryptography (ECC)
Elliptic Curves, ECC and ECDSA, Sign, Verify

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 Uses a pair of keys: public key + private key
 Sign / decrypt by private key
 Verify / encrypt by public key
Public ...

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 Well-known public-key crypto-systems
 RSA – based on discrete logarithms
 ECC – based on elliptic curves
 ECC crypt...

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 Public / private key cryptography
based on the algebraic structure of
elliptic curves over finite fields
 Requires sm...

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 Elliptic curves cryptography (ECC)
 Uses ecliptic curves over the finite
field Fp (p is prime, p > 3)
 A set of inte...

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 A point G over the curve can be
multiplied by an integer k
 P = k * G
 The result is another point P
staying on the...

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Elliptic Curves Multiplication in Python
from pycoin.ecdsa import Point
from pycoin.ecdsa import CurveFp
curve = CurveF...

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 The elliptic curves over Fp
 Have at most 2 points per y
coordinate (odd x and even x)
 A public key P(x, y) can be...

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 ECC operates with a set of EC domain parameters:
 T = (p, a, b, G, n, h)
 Prime field (prime p), elliptic equation ...

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 The private key in secp256k1 is 256-bit integer (32 bytes)
 Example of Ethereum private key (encoded as 64 hex digit...

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 The blockchain address in Ethereum is 20 bytes
 Calculated as: last20bytes(keccak256(publicKeyFull))
 Example of Et...

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Ethereum Key to Addresses – Example
pip install eth_keys
import eth_keys, binascii
privKey = eth_keys.keys.PrivateKey(b...

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 Ethereum uses secp256k1-based ECDSA signatures
 ECDSA generates deterministically a random point R (see RFC6979)
 E...

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Sign Message in Ethereum – Example
import eth_keys, binascii
privKey = eth_keys.keys.PrivateKey(binascii.unhexlify(
'97...

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Verify Message Signature in Etherscan
 Verify message signature at https://etherscan.io/verifySig by:
 signer address...

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Verify Ethereum Signature – Example
import eth_keys, binascii
msg = b'Message for signing'
msgSigner = '0xa44f70834a711...

Hashing and Hash Functions
Cryptographic Hash Functions

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What is Cryptographic Hash Function?
Some text
Some text
Some text
Some text
Some text
Some text
Some text
20c9ad97c081...

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Cryptographic Hash Function
 One-way hash function
 Infeasible to invert
 Extremely little chance
to find a collision

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 Old hash algorithms: MD5, SHA-0, SHA-1
 Withdrawn due to cryptographic weaknesses (collisions found)
 SHA-2
 Famil...

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 BLAKE / BLAKE2 / BLAKE2s / BLAKE2b
 Fast, secure cryptographic hash function
 256-bit (BLAKE-256, BLAKE2s) and 512-...

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Calculating Hash Functions in Python
import hashlib, binascii
text = 'hello'
data = text.encode("utf8")
sha256hash = ha...

HMAC and Key Derivation
MAC, HMAC, PBKDF2 and SCrypt

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 HMAC = Hash-based Message Authentication Code
 HMAC(key, msg, hash_func)  hash
 Message hash mixed with a secret s...

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HMAC Calculation in Python – Example
import hashlib, hmac, binascii
def hmac_sha256(key, msg):
return hmac.new(key, msg...

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 Scrypt (RFC 7914) is a strong cryptographic key-derivation function
 Memory intensive, designed to prevent ASIC and ...

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Scrypt Key Derivation in Python – Example
import scrypt, os, binascii
passwd = "p@$$w0rD~3"
salt = os.urandom(32)
print...

Blockchain Cryptography and Wallets
Keys, Addresses, Signatures, Wallets

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Public / Private Keys, Wallets & Blockchain
private key public key address
transaction
sign by private key
signed
trans...

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 In blockchain wallets keep private keys, highly encrypted
 Simple wallet (keystore) keeps a single private key
 Exa...

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 The BIP-32 standard defines how a crypto-wallet can generate
multiple keys + addresses
 The wallet is initialized by...

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 Most modern crypto wallets start from a 512-bit securely
generated random seed (see the BIP-39 standard)
 The seed (...

BIP-39 Mnemonic
Seed Generator
Live Demo
https://iancoleman.io/bip39

Wallet Encryption and AES
AES, CBC/CTR, Padding, Scrypt, HMAC

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 A single secret key to
encrypt / decrypt
 The secret key is usually
derived by a password
 Both the sender and the
...

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 AES is a "block cipher" – encrypts block by block (e.g. 128 bits)
 It has several modes of operation (CBC, ECB, CTR,...

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Example: AES Encrypt / Decrypt in Python
import pyaes, pbkdf2, binascii, os, secrets
plaintext = "Sample text for encry...

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Ethereum UTC / JSON Wallet Encryption
{ "version": 3, "id": "…", "address": "b97e993872a9050c07f…ef195",
"Crypto": {
"c...

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Blockchain Cryptography for Devs

License
 This course (slides, examples, demos, videos, homework, etc.)
is licensed under the "Creative Commons Attributio...

Trainings @ Software University (SoftUni)
 Software University – High-Quality Education,
Profession and Job for Software ...

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