Cryptography donors #

“So do you roll your own crypto?” #

If you’re reading this section, you might already know the short answer: No.

We don’t roll our own crypto. Themis relies on algorithm implementations that come from platform providers and open-source projects. We believe that anyone in their right mind should use well-known, audited implementations of well-known and proven cryptographic ciphers for their core security needs.

We’ve built Themis to have easy-to-use large building blocks bound to precise security guarantees and use cases—these are Secure Cell, Secure Message, Secure Session, and Secure Comparator cryptosystems. They are composed according to the best modern practices of achieving certain security guarantees.

What should you use #

Soter uses cryptographic algorithms provided by cryptography donors (or backends). Currently, all of them come from one family of products based on OpenSSL:

• OpenSSL
• LibreSSL
• BoringSSL

However,

1. The libcrypto library provided by these products does not contain all the primitives we need.

   For example, Secure Comparator relies on ed25519, and in the future we might require even more esoteric elliptic curves.

   We have to supply some primitives from different backends.

2. Some considerations about performance and implementation elegance made us build additional experimental backends:

   • BearSSL
   • libsodium
   • CommonCrypto

Choosing a backend #

What to use as a backend is a matter of personal preferences and specific constraints of the task at hand. Since Themis 0.9.5 the build system enables you to choose a different backend yourself when building Themis.

Our goal is not only to keep developing Themis with the best implementations of the best cryptographic algorithms available under the hood. Our goal lies as much in being able to consciously choose the optimal cryptographic algorithms for each use case, on every Themis build.

On leaving OpenSSL #

We rely on the following list of crypto-primitives and ciphers for Themis:

• AES
• CSPRNG
• ECDSA, ECDH
• PBKDF
• RSA
• SHA, HMAC

We consider OpenSSL, LibreSSL, and BoringSSL to be crypto-engines that fully support these crypto-primitives and ciphers on Linux, macOS, Windows, iOS and Android. However, we’re planning to move away from using OpenSSL everywhere some day and use BoringSSL as the default crypto engine on every platform supported by Themis.

As the algorithm choice for Themis stabilises, we plan to migrate away from the libcrypto dependency as well.

You can check out our plans concerning the support and migration to BoringSSL in the list of issues.