Constant-time programming
Constant-time programming is the practice of designing algorithms whose execution behavior does not depend on secret data or varying input values.
Hacking Cryptography
A constant-time implementation is software or hardware whose execution behavior does not depend on secret-dependent values or control flow.
- How it is used
- Protects cryptographic operations from timing attacks and side-channel analysis by removing secret-dependent execution differences.
- How deep it goes
- Explains power-analysis failures, ladder operations, and branchless control flow, while deferring many Montgomery optimization details.
- Examples
- Uses RSA exponentiation traces, the Montgomery ladder, and GCC inline-assembly summation with conditional moves.
- What you can do after
- Apply it via fixed-operation algorithms, branchless control flow, and constant-time validation for sensitive cryptographic inputs.
Read how Hacking Cryptography explains constant-time programming →
Real-World Cryptography
A constant-time algorithm executes in a pattern whose duration does not depend on secret data.
- How it is used
- Defends sensitive cryptographic computations against timing and related software side-channel attacks.
- How deep it goes
- Explains branch-free comparisons and algorithmic patterns, while stopping short of formal proofs or implementation-level completeness.
- Examples
- Uses Go authentication-tag comparison, Montgomery’s ladder, and RSA square-and-multiply-always.
- What you can do after
- Apply it by removing secret-dependent branches and memory accesses from cryptographic implementations.
Read how Real-World Cryptography explains constant-time programming →
Related concepts
- timing attackaddresses · A timing attack is a side-channel attack that infers information, often secret data, by measuring differences in the time taken to process inputs or perform computations.
- conditional moveuses · A conditional move is a processor instruction that transfers a value when a Boolean predicate holds without branching to a different instruction path.
- side-channel attackaddresses · A side-channel attack infers secret information from unintended physical or operational leakage produced by a system’s implementation rather than its intended outputs.
- cache attackaddresses · A cache attack infers a victim's secret-dependent computation by observing the timing or state changes of shared processor memory caches.
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