Short answer: BIKE (Bit Flipping Key Encapsulation) is a code-based key encapsulation mechanism built on quasi-cyclic moderate density parity-check (QC-MDPC) codes, and it was submitted to the NIST Post-Quantum Cryptography Standardization Process. Its specification says the codes can be decoded with bit-flipping techniques. This article summarises the design from the project site, its Round 2 specification and a 2023 implementation survey, and makes no claim about any real-world use.
What BIKE is
The BIKE project site describes it as a code-based key encapsulation mechanism based on QC-MDPC codes, submitted to the NIST Post-Quantum Cryptography Standardization Process. The Round 2 specification, dated 30 June 2019, describes BIKE as a suite of algorithms for key encapsulation based on QC-MDPC codes that can be decoded using bit-flipping decoding techniques. It says the document highlights security, performance and simplicity advantages that, in the submitters' words, make BIKE a compelling candidate for post-quantum key encapsulation standardization. That is the designers' own assessment.
Bit-flipping decoding
The specification has a section on decoding with the bit-flipping algorithm, which it calls particularly interesting among the available decoding approaches. It says it proposes two variants of the bit-flipping algorithm corresponding to different trade-offs, one for each of the CPA and CCA settings. The material we reviewed does not describe those trade-offs in detail, so we do not either.
The variants
The specification presents three IND-CPA secure variants, BIKE-1, BIKE-2 and BIKE-3, which it says follow either the McEliece or the Niederreiter framework, each with some important differences. It also has a section on IND-CCA variants, including BIKE-1-CCA and BIKE-3-CCA.
Implementations
The project site lists a constant-time software implementation, a reference software implementation and a hardware implementation, along with a specification document dated 10 October 2024 and known-answer test files. A 2023 paper in OASIcs, from the PARMA-DITAM workshop, provides an overview and comparison of existing state-of-the-art implementations of the BIKE QC-MDPC code-based KEM, which it calls a candidate in NIST's standardization process. It considers software, hardware and mixed hardware-software implementations and evaluates their performance and, for hardware, resource utilization. Its funding note mentions a company and EU and research-centre support.
Where it sits among post-quantum schemes
BIKE is one of several approaches submitted to the NIST process. The 2023 survey describes the process as aiming at cryptosystems that resist attacks by both traditional and quantum computers and could substitute for traditional public-key cryptography, which it says is expected to be broken by quantum computers in the next decades. That is the survey's framing, and it is a statement about expectations, not a date.
What this does not tell you
These sources do not say whether NIST will standardize BIKE, and this article does not state the outcome. We do not give performance numbers, key sizes or security levels, and the material reviewed does not include them. Check the current specification before relying on any parameter.
FAQ
What is BIKE?
A code-based key encapsulation mechanism based on QC-MDPC codes, submitted to the NIST Post-Quantum Cryptography Standardization Process.
What does bit flipping mean here?
It is the decoding technique the specification says can be used to decode QC-MDPC codes.
What variants exist?
The Round 2 specification presents BIKE-1, BIKE-2 and BIKE-3 as IND-CPA secure variants, and IND-CCA variants such as BIKE-1-CCA and BIKE-3-CCA.
Are there implementations?
The project site lists constant-time software, reference software and hardware implementations, and a 2023 paper compares software, hardware and mixed implementations.
Is BIKE a NIST standard?
These sources describe it as a submission and candidate. They do not state a standardization outcome.
All field notes