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Password-protected data made easy.

Project description

Privy is a small and fast utility for password-protecting secret data such as API keys, cryptocurrency wallets, or seeds for digital signatures.

Table of Contents


Say for example you are using GnuPG. You are about to sign a message but it first requires your password. Does your password become the input to instantiate your private key? No, it is first hashed by a secure key derivation function. That hash then becomes the input to a symmetric cipher such as AES which then decrypts your stored private key. That is what Privy does.

Fear not! With Privy, this become trivially easy:

>>> import privy
>>> # After creating secret, immediately encrypt it using Privy.
>>> data = b'secret'
>>> hidden = privy.hide(data, ask_for_password())
>>> hidden

Now you can safely store or transmit the hidden secret. Whenever your user needs to use their secret again, ask for their password to take a peek.

>>> privy.peek(hidden, password)


Privy is available on Linux/macOS and Windows and supports Python 2.7, 3.3+, PyPy, and PyPy3.3-5.5+.

$ pip install privy

Encryption scheme

Secrets are encrypted using the Fernet protocol. Specifically, it uses AES for encryption and has built-in authentication using HMAC. The private key used for encryption is derived from the password using a key derivation function. The key derivation function used is Argon2, the winner of the Password Hashing Competition. Both Argon2i and Argon2d variants are supported.

Encrypted format

ascii(Argon2 algorithm || security level || base64(salt) || base64(Fernet token))


There are 2 functions: hide and peek.


hide(secret, password, security=2, salt=None, server=True)

Encrypts secret using password. Returns the hidden secret as unicode.

  • Parameters

    • secret (bytes) - The secret to encrypt.

    • password (bytes or unicode) - The password used to access the secret.

    • security (int) - A number 0-20 inclusive. Higher values are more secure at the cost of slower computation and greater use of memory. See security levels.

    • salt (bytes) - The salt used for the password hash. Defaults to os.urandom(32).

    • server (bool) - If True, it is assumed side-channel attack protection is needed and therefore the Argon2i algorithm will be used. Otherwise, the password will be hashed using the Argon2d algorithm.


peek(hidden, password, expires=None)

Decrypts hidden using password. Returns the secret as bytes.

  • Parameters

    • hidden (bytes or unicode) - The hidden secret to decrypt.

    • password (bytes or unicode) - The password used to access the secret.

    • expires (int) - The maximum number of seconds since encryption that is allowed. The default is no expiration.

A ValueError will be raised if the password is wrong, the password was attempted on a different hidden secret, or the number of seconds since encryption is > expires argument.

Security levels

All expected times were taken from tests on an Intel Core i7-2670QM @ 2.2 GHz when decrypting a 256 KiB secret.

This is the command, where SL is the desired security level:

$ python -m timeit -s "import privy, os; pw = 'password'; s = os.urandom(1024 * 256); h = privy.hide(s, pw, SL)" "privy.peek(h, pw)"


Argon2 settings

Expected time



m=8 KiB, t=1

7 msec

Lowest possible


m=4 MiB, t=10

54 msec


m=8 MiB, t=10

99 msec



m=32 MiB, t=10

367 msec


m=48 MiB, t=10

540 msec


m=96 MiB, t=10

1.1 sec

Good choice


m=256 MiB, t=10

3 sec


m=512 MiB, t=10

6 sec


m=768 MiB, t=10

9 sec


m=1 GiB, t=10

12.2 sec


m=2 GiB, t=20

48 sec

For use on users’ machines


m=3 GiB, t=30



m=4 GiB, t=40



m=5 GiB, t=50



m=6 GiB, t=60



m=7 GiB, t=70



m=8 GiB, t=80



m=9 GiB, t=90



m=10 GiB, t=100



m=11 GiB, t=110



m=12 GiB, t=120



Privy is distributed under the terms of either

at your option.


Important changes are emphasized.


  • Breaking: Support for Python 3.3 has been dropped.


  • Breaking: Privy is now dual-licensed under the terms of MIT and Apache v2.0.

  • Only documented methods hide and peek are now exposed in the root namespace.

  • Travis now runs tests with the latest versions of PyPy and PyPy3.

  • Improvements to documentation.


  • Breaking: For saner conformity, security level 7 now utilizes 512 MiB of RAM instead of 448.

  • Major improvements to documentation.


  • Added security levels 11-20. These are quite resource intensive and are therefore only acceptable for individual use.


  • Breaking: Due to requests, the encrypted format now uses url-safe base64 instead of hex.


  • Initial release

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