Important note: KeyCzar has some known security issues which may influence your decision to use it. See Known Security Issues.
Keyczar is an open source cryptographic toolkit designed to make it easier and safer for developers to use cryptography in their applications. Keyczar supports authentication and encryption with both symmetric and asymmetric keys. Some features of Keyczar include:
- A simple API
- Key rotation and versioning
- Safe default algorithms, modes, and key lengths
- Automated generation of initialization vectors and ciphertext signatures
- Java, Python, and C++ implementations
- International support in Java
Keyczar was originally developed by members of the Google Security Team and is released under an Apache 2.0 license.
Cryptography is easy to get wrong. Developers can choose improper cipher modes, use obsolete algorithms, compose primitives in an unsafe manner, or fail to anticipate the need for key rotation. Keyczar abstracts some of these details by choosing safe defaults, automatically tagging outputs with key version information, and providing a simple programming interface.
Keyczar is designed to be open, extensible, and cross-platform compatible. It is not intended to replace existing cryptographic libraries like OpenSSL, PyCrypto, or the Java JCE, and in fact is built on these libraries.
An illustrative use case
Suppose an application needs to encrypt a URL parameter value with a symmetric key. Normally, a developer would need to decide which algorithm to use, the key length to use, the mode of operation, how to handle initialization vectors, how to rotate keys, and how to sign ciphertexts. Keyczar simplifies these choices. Using an existing keyset, a Java developer would need to call the following:
Crypter crypter = new Crypter("/path/to/your/keys"); String ciphertext = crypter.encrypt("Secret message");
Similarly a Python developer would call the following:
crypter = Crypter.Read("/path/to/your/keys") ciphertext = crypter.Encrypt("Secret message")
Interested in getting involved? We encourage open source developers to contribute to the Keyczar project. Please join us on the Keyczar project and subscribe to the Keyczar discussion group.
Known Security Issues
The following section lists known security issues.
There are probably others that have not been identified.
Use of SHA 1 and 1024 bit DSA
Keyczar uses 1024 bit DSA keys with SHA1. Both of these are considered weak by current security standards. However, it is not trivial to upgrade without breaking backwards compatibility.
Signed Session Encryption Re-signing
Keyczar signed session encryption does not include the key ID of the signing key inside the encrypted plaintext. This makes it possible for an attacker to strip the signature from a message, and re-sign it using their private key, making it look like they sent the original message.
DSA Signature Malleability
DSA signatures are basically two variable length ints. So some DSA signatures are shorter than others.
There was a bug in KeyCzar (fixed here) which essentially padded (right padding with 0) all DSA signatures to their maximum length.
Some crypto libraries - including many JCE implementations - stop checking the signature after finding both ints, which means that they will verify signature that have extra data. This is why keyczar did not discover the extra data in DSA signatures.
However, this can be a problem for specific crypto applications that compute fingerprints of data that includes a message and its signature. See the CVN, OpenSSL's comments and [problem](and https://en.bitcoin.it/wiki/Transaction_Malleability) this causes for BitCoint.
Some new JCE implementations are more strict - and will reject DSA signatures with extra data. In order for older (improperly padded DSA signatures) to be acceptible even when running KeyCzar on such new JCE implementations - the KeyCzar Java DSA verifier function trims any extra data from the signature.
Note that this means you should not use this implementation for such applications - such as bitcoin - without setting the "keyczar.strict_dsa_verification" system property.
As other underlying crypto libraries make this strict - it is probable that other language implementations may have this issue.