One-Time Password (HOTP)
Description

Use a 2-character alphanumeric challenge to generate & verify with a corresponding 2-character response.

Provides higher entropy (security) than authentication tables while using less bandwidth & being easier to use.

Challenge-Response:

A->B: AUTH AA

(B inputs AA and sends response with new challenge)

B->A: ANS BB. AUTH CC

(A verifies response; provides response to new challenge)

A->B: ANS DD

(B verifies response)

--
Authentication Tables
Description

Challenge-response tables for authentication.

Challenge-Response:

A->B: AUTH CEY

(B look up response for table: Charlie, column: E, row: Y; sends new challenge)

B->A: ANS 7. AUTH AIT

(A verifies response; sends response for new challenge, table: Alpha, column: I, row: T)

A->B: ANS T

(B verifies response)

One-Time Pad
Description

Use a 5-digit key to generate a fixed (paper friendly) or streamed (more secure) cipher.

Cipher values are added to ASCII encoded message to create encrypted message. All values are 3-digit for manual calculations.

When encoding exceeds 999, only keep the last 3 digits. When decoding goes negative, add 1000.

Encoding (with overflow example): 
Key: 12345
234 967 890 112 314...

Message:   H     E     L     L     O
ASCII:     072   069   076   076   079
Cipher:  + 234   967   890   112   314
         ─────────────────────────────
Result:    306  1036   966   188   393
Encoded:   306   036   966   188   393
Decoding (with negative handling): 
Key: 12345
234 967 890 112 314...

Encoded:   306   036   966   188   393
Cipher:  - 234   967   890   112   314
         ─────────────────────────────
Result:    072  -931   076   076   079
ASCII:     072   069   076   076   079
Message:     H     E     L     L     O
ASCII Reference Table