com.google.crypto.tink.prf.Prf Maven / Gradle / Ivy
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// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
////////////////////////////////////////////////////////////////////////////////
package com.google.crypto.tink.prf;
import com.google.errorprone.annotations.Immutable;
import java.security.GeneralSecurityException;
/**
* The PRF interface is an abstraction for an element of a pseudo random function family, selected
* by a key. It has the following properties:
*
* - It is deterministic: PRF.compute(input, length) will always return the same output if the
* same key is used. PRF.compute(input, length1) will be a prefix of PRF.compute(input, length2) if
* length1 < length2 and the same key is used. - It is indistinguishable from a random function:
* Given the evaluation of n different inputs, an attacker cannot distinguish between the PRF and
* random bytes on an input different from the n that are known.
*
*
Use cases for PRF are deterministic redaction of PII, keyed hash functions, creating sub IDs
* that do not allow joining with the original dataset without knowing the key. While PRFs can be
* used in order to prove authenticity of a message, using the MAC interface is recommended for that
* use case, as it has support for verification, avoiding the security problems that often happen
* during verification. It also allows for non-deterministic MAC algorithms.
*/
@Immutable
public interface Prf {
/**
* Computes the PRF selected by the underlying key on input and returns the first outputLength
* bytes.
*
* @param input the input to compute the PRF on.
* @param outputLength the desired length of the output in bytes. When choosing this parameter
* keep the birthday paradox in mind. If you have 2^n different inputs that your system has to
* handle set the output length to ceil(n/4 + 4) This corresponds to 2*n + 32 bits, meaning a
* collision will occur with a probability less than 1:2^32. When in doubt, request a security
* review.
* @throws GeneralSecurityException if the algorithm fails or if the output of algorithm is less
* than outputLength.
*/
byte[] compute(byte[] input, int outputLength) throws GeneralSecurityException;
}