# Hash Functions - Examples

In this section we shall provide a few **examples** about calculating cryptographic hash functions in Python.

## Calculating Cryptographic Hash Functions in Python

We shall use the standard Python library `hashlib`. The input data for hashing should be given as **bytes sequence** (bytes object), so we need to **encode the input string** using some text encoding, e.g. `utf8`. The produced **output data** is also a bytes sequence, which can be printed as hex digits using `binascii.hexlify()` as shown below:

```python
import hashlib, binascii

text = 'hello'
data = text.encode("utf8")

sha256hash = hashlib.sha256(data).digest()
print("SHA-256:   ", binascii.hexlify(sha256hash))

sha3_256 = hashlib.sha3_256(data).digest()
print("SHA3-256:  ", binascii.hexlify(sha3_256))

blake2s = hashlib.new('blake2s', data).digest()
print("BLAKE2s:   ", binascii.hexlify(blake2s))

ripemd160 = hashlib.new('ripemd160', data).digest()
print("RIPEMD-160:", binascii.hexlify(ripemd160))
```

Run the above code example: <https://repl.it/@nakov/Hashes-SHA2-SHA3-BLAKE2-RIPEMD-in-Python>.

The expected **output** from the above example looks like this:

```
SHA-256:    b'2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824'
SHA3-256:   b'3338be694f50c5f338814986cdf0686453a888b84f424d792af4b9202398f392'
BLAKE2s:    b'19213bacc58dee6dbde3ceb9a47cbb330b3d86f8cca8997eb00be456f140ca25'
RIPEMD-160: b'108f07b8382412612c048d07d13f814118445acd'
```

Calculating `Keccak-256` hashes (the hash function used in the Ethereum blockchain) requires non-standard Python functions. In the below example we use the `pycryptodome` package available from PyPI: <https://pypi.org/project/pycryptodome>.

First install "pycryptodome" (<https://www.pycryptodome.org>)

```python
pip install pycryptodome
```

Now write some Python code to calculate a **Keccak-256** hash:

```
from Crypto.Hash import keccak
import binascii

keccak256 = keccak.new(data=b'hello', digest_bits=256).digest()
print("Keccak256:", binascii.hexlify(keccak256))
```

Run the above code example: <https://repl.it/@nakov/Keccak256-in-Python>.

The **output** from the above examples is:

```
Keccak256: b'1c8aff950685c2ed4bc3174f3472287b56d9517b9c948127319a09a7a36deac8'
```


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