Overview
A one-time pad can hide plaintext perfectly only when the pad is random, secret, as long as the message, and never reused.
CoreSource checked
One-Time Pad
Encrypts a message by combining it with a truly random key used exactly once.
Quick Facts
Compact metadata for implementation and discovery.
- Category
- Cryptography
- Difficulty
- Beginner
- Family
- Symmetric Encryption
- Tier
- Core
- Status
- Verified
- Review
- Source Checked
- Sources
- 1
- Formulas
- 1
- Relationships
- 1
- Code example
- Ready
- Visualization
- Ready
Core Concepts
secret padxor encryptionsingle useperfect secrecymisuse resistanceparameter validation
Quick facts
Complexity
Runtime and memory behavior at a glance.
Best
O(n)
Average
O(n)
Worst
O(n)
Space
O(n)
When to Use
- Use when protecting messages needs secret pad.
- Use when the input matches the assumptions behind symmetric Encryption.
When Not to Use
- Avoid when a well-reviewed library already provides the primitive for production use.
- Avoid when a simpler algorithm gives the required result with less setup.
What It Does
- Encrypts a message by combining it with a truly random key used exactly once
- Uses secret pad and xor encryption to guide the work.
- Produces ciphertext, digest, proof, or derived key.
Use Cases
- Protecting messages
- Authenticating data
- Deriving or managing cryptographic material
Inputs
- Secret key or public parameters
- Message or secret data
- Nonce, salt, or context where needed
Outputs
- Ciphertext, digest, proof, or derived key
Key Formulas (1)
One-time pad encryption
ciphertext = plaintext xor pad
ciphertext = plaintext xor padCombines each message bit with the matching random pad bit.
Pseudocode
- 1.Validate keys, nonces, salts, group parameters, and input ranges
- 2.Apply the primitive's block, hash, group, or reduction operation
- 3.Combine intermediate values exactly as the construction specifies
- 4.Return the protected value, proof, signature, derived key, or verification result
Canonical Example
- Input
- message = 'pay 10' with configured keys, nonces, or public parameters
- Output
- Ciphertext, digest, proof, or derived key
- Explanation
- One-Time Pad applies secret pad to produce ciphertext, digest, proof, or derived key.
Implementation Notes
- Use constant-time library implementations for real systems instead of hand-written primitives.
- Keep the secret pad step separate enough to test independently.
- Use reviewed libraries and protocol specifications for production security-sensitive code.
Common Pitfalls
- Reusing nonces, salts, pads, or domain parameters can destroy the intended security property.
- Test edge cases, not only clean examples.
- Treating educational pseudocode as production crypto can hide nonce, parameter, and side-channel requirements.
Interactive Mechanism Walkthrough
Graph Frontier & Edge RelaxationShow the major cryptographic rounds or data dependencies without exposing secrets.
Step 1 of 4: Validate keys, nonces, salts, group parameters, and input ranges
cryptography-mechanismNotes
One-Time Pad should be used with the assumptions and tradeoffs of symmetric Encryption in mind.
Sources (1)
What each reference supports for this entry.
Handbook of Applied Cryptography
BookCryptography reference covering perfect secrecy and one-time pad requirements.
Open sourceExplore Next
Good next jumps from the relationship graph, ranked for useful discovery.
Relationships
View full relationship pageConceptual neighborAES
Both are symmetric encryption methods, but the one-time pad requires single-use random keys.
Related Algorithms
Tags
CryptographySymmetric KeySecurityClassic