- DeveloperWorks blogs allow community members to share thoughts and expertise on topics that matter to them, and engage in conversations with each other. You can browse for and follow blogs, read recent entries, see what others are viewing or recommending, and request your own blog.
- AES-128 has 128 bit key = 16 bytes. Randomkey = os.urandom(16) should be sufficient for most uses. When you feed this random value to M2 (or whatever crypto library), it is transformed internally into a 'key schedule' actually used for encryption.
- Unfortunately, what is considered sufficient will necessarily increase as computers get more powerful and able to make more guesses in a shorter period. As of 2015, it is believed that 32 bytes (256 bits) of randomness is sufficient for the typical use-case expected for the secrets module.
HDWallet: Secure, hierarchical Bitcoin wallet generation
The implementation is based on the proposal BIP 0032 and is currently in audit mode. Please do not use in production yet. Testing welcome.
A common problem for Bitcoin enabled webservices is secure storage of user funds. Usually one generates for each new user an own address to track what user owns which coins.
In python i'm using the Crypto package to generate a random number of length 256 bit. The function for doing so is import Crypto.Random.random as rand key = rand.getrandbits(256.
The classic generation of a new bitcoin address requires basically 3 steps:
- Generate a large 256-bit number from a (P)RNG (= private key)
- Calculate the ECC public key for that number (= public key)
- Do some hashing and encoding on the pubkey (= bitcoin address)
Python Generate 256 Bit Key
If the webserver gets hacked and the private keys are stored on it an attacker can steal all user funds.
However, it is not possible to use the private key in the place of the public key. 
If the locking key is private, this system makes it possible to verify that the owner locked those documents. The reason is that a message encrypted by the sender can only be opened by a person with the matching public key, thus verifying that the sender did actually hold the private key.
Address generation without a private key
Based on the mathematical properties of ECC we can apply equivalent operations on a private key and its public key. The resulting keys will be a new corresponding keypair. In pseudocode:
We apply the operation on the public key on the webserver to generate new bitcoin addresses no private key is needed.To spend the funds later, we derive the private for the address in a secure, offline environment.
For creating a hierachical wallet structure we use the child derivation function described in BIP 0032.
Installation
What Is 256 Bit
Code example
Generate 256 Bit Key Python Tutorial
The code above produces the following output