The work on Tink is guided by the design goals discussed below. To get a quick overview of Tink design you can also take a look at slides from a talk about Tink presented at Real World Crypto 2019.
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Security Tink is built on top of existing libraries such as BoringSSL and Java Cryptography Architecture, but includes countermeasures to many weaknesses in these libraries, which were discovered by Project Wycheproof, another project from our team.
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Easiness Most crypto operations such as data encryption, digital signatures, etc. can be done with only a few lines of code. Tink's interfaces abstract away from the underlying implementations. Interfaces are usable without knowing the underlying class that implements it.
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Hard-to-misuse Tink aims to eliminate as many potential misuses as possible. For example, if the underlying encryption mode requires nonces and is insecure if nonces are reused, then Tink does not allow the passing of nonces by the user. Interfaces have security guarantees that must be satisfied by each primitive implementing the interface. This may exclude some encryption modes. Rather than adding them to existing interfaces and weakening the guarantees of the interface it is possible to add new interfaces and describe the security guarantees appropriately.
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Readability Tink shows the security guarantees (e.g., safe against chosen-ciphertext attacks) right in the interfaces, allowing security auditors and automated tools to quickly discover usages where the security guarantees don’t match the security requirements. Tink also separates APIs for potential dangerous operations (e.g., loading cleartext keys from disk), allowing discovering, restricting, monitoring and logging their usages.
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Extensibility Tink makes it easy to support new primitives, new algorithms, new ciphertext formats, new key management systems, etc.
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Agility Tink provides built-in crypto agility. It supports key rotation, deprecation of obsolete schemes and adaptation of new ones. For example, if an implementation of a crypto primitive is found broken, you can switch to a different implementation by rotating keys, without changing or recompiling code.
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Interoperability Tink produces and consumes ciphertexts that are compatible with existing crypto libraries. Tink supports encrypting or storing keys in Amazon KMS, Google Cloud KMS, Android Keystore, iOS Keychain, and it is easy to add support for custom key management systems.
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Versatility No part of Tink is hard to replace or remove. All components are recombinant, and can be selected and assembled in various combinations. For example, if you need only digital signatures, you can exclude symmetric key encryption components.