BaseHash 2.2.1

BaseHash
========

[](https://travis-ci.org/bnlucas/python-basehash)

BaseHash is a small library for creating reversible obfuscated identifier hashes
to a given base and length. The project is based on the GO library, [PseudoCrypt][pc]
by [Kevin Burns][kb]. The library is extendible to use custom alphabets and other
bases.

The library uses golden primes and the [Baillie-PSW][bp] primality test for hashing
to `n` length. From testing, I have gotten `base62` up to `171` in length.

```
Maximum number is Base^Length - 1.
-> 62^171 - 1 or 315485137315301582773830923281251564555089304044116975095028710
008180170985809814948409129256031320171601473029340987051144213
425607224233134700199050224309707192084206558324823774511143549
765069844412467187455459156942237963528166277256376429656681225
8180788198965409784329587392583208081351811265973977087
```


Install
-------

```
pip install basehash
```

Testing
-------

```
nosetests tests/
```

Encode
------
```python
import basehash

base62 = basehash.base62()

encoded = base62.encode(2013)
decoded = base62.decode('WT')

print encoded, decoded
```
```
WT 2013
```

Hash
----
```python
import basehash

base62 = basehash.base62()

hashed = base62.hash(2013, 8)
unhashed = base62.unhash('6LhOma5b')

print hashed, unhashed
```
```
6LhOma5b 2013
```

Generating your own primes
--------------------------
The `GENERATOR` variable uses the golden ratio, `1.618033988749894848`, to get
the next highest prime of `base ** number * generator`. This can be overridden
within the base classes.

```python
import basehash

base62 = basehash.base62(1.75) # base62(generator=1.75)
```

Generating your own alphabets
-----------------------------

```python
import basehash

alphabet = basehash.generate_alphabet(basehash.BASE36, randomize=20)
# runs random.shuffle on basehash.BASE36 (randomize)=20 times.
# produces something like: L0RJBY2HQ7MSGXPE6NCUW38KAFVDO51IZ94T
# save this alphabet to use for hasher.unhash()

hasher = basehash.base(alphabet, length=10)
```

Maximum number while hashing
----------------------------
There is a maximum number while hashing with any given base. To find out what
this number is, we use the `Base^Length - 1`.

```python
import basehash

base36 = basehash.base36()

print base36.maximum_value(12) # or base36.maximum(length)
```
```
4738381338321616895
```

So with the max number for `base36` at length `12` as `4738381338321616895` we
get the following:

```python
import basehash

base36 = basehash.base36()

hash = base36.hash(4738381338321616895, 12)
# 'DR10828P4CZP'

hash = base36.hash(4738381338321616896, 12)
# ValueError: Number is too large for given length. Maximum is 36^12 - 1.
```

Extending
---------
Extending is made easy with some time spent determining the next highest prime
dynamically, the fastest possible that I have been able to make it so far.

```python
import basehash

custom = basehash.base('24680ACEGIKMOQSUWYbdfhjlnprtvxz')

print custom.encode(2013) # 66x
print custom.decode('66x') # 2013
print custom.hash(2013, 8) # 8AQAQdYd
print custom.unhash('8AQAQdYd') # 2013
print custom.maximum_value(12) # 787662783788549760
```

[pc]: https://github.com/KevBurnsJr/pseudocrypt
[kb]: https://github.com/KevBurnsJr
[bp]: http://en.wikipedia.org/wiki/Baillie-PSW_primality_test


2.2.1 (2015-05-28)
==================

- Implemented [six](https://bitbucket.org/gutworth/six) to allow use of `xrange`
in Python 2 and `range` in Python 3

2.2.0 (2015-05-14)
==================

- Fixed ussues with python 3.4

2.1.0 (2013-07-24)
==================

- Create custom random alphabets using `basehash.generate_alphabet(alphabet)`.

- BaseHash.base now checks `alphabet` for duplicates using `set`.

2.0.2 (2013-07-10)
==================

- base and baseN now accept a length parameter, defaulted to HASH_LENGTH so that
baseN.hash(num, length) is set globally, not locally.

2.0.0 (2013-07-07)
==================

- Moved everything to an object. Removed baseN.py files, allows for easier
configuration of `GENERATOR` and for extending to a custom alphabet.

1.0.7 (2013-07-06)
==================

- There was an issue with hashes sometimes being returned one to two charcters
shorter than `length`, causing `base.base_unhash` to not function properly. To
fix this, the hashes are right-padded with `alphabet[0]`.

- Since `0` raises an error inside `primes.invmul`, `base.base_unhash` is unable
to unhash it. To allow the start of your number sequence to be `0` instead of
`1`, if needed, hashing `base.base_hash(0, length=6)` will return
`''.rjust(length, alphabet[0])`.

1.0.6 (2013-06-29)
==================

- Fixed issues with setup.py. First time using a setup.py within a package,
first time publishing the library outside of GitHub.

1.0.5 (2013-06-28)
==================

- Added nose unittests.

1.0.4 (2013-06-28)
==================

- Added setup.py, LICENSE, HISTORY.rst, and .travis.yaml.

1.0.3 (2013-06-27)
==================

- Added a simple test for `prime < 31` to reduce calculation time.

- Fixed issue of `strong_pseudoprime(n, 3)` giving false results.

1.0.2 (2013-06-27)
==================

- Changed primality test from Miller-Rabin to Baillie-PSW. This algorithm is
significantly faster.

- Changed determination to use `sqrt(n)` or `isqrt(n)` to an improved version of
`isqrt(n)`.

- BaseHash is now PEP compliant.

1.0.1 (2013-06-25)
==================

- Changed primality test from Fermat to Miller-Rabin. Improved accuracy on false
results when it comes to pseudoprimes.

1.0.0 (2013-06-24)
==================

- Released code to GitHub repository python-basehash
https://github.com/bnlucas/python-basehash

0.0.1 (2013-06-23)
==================

- Initialization