Keyword Alphabet Builder

Build an A–Z keyword substitution alphabet by taking distinct keyword letters first and appending unused letters.

Description

A keyword substitution alphabet puts the distinct letters of a keyword first and fills the remaining positions with unused alphabet letters.

A keyword substitution alphabet puts the distinct letters of a keyword first and fills the remaining positions with unused alphabet letters. The ordering creates a 26-letter mapping while repeated keyword letters contribute only once.^[1]

Build an A–Z keyword substitution alphabet by taking distinct keyword letters first and appending unused letters.

When to use Keyword Alphabet Builder

Use this tool to build an A–Z keyword substitution alphabet by taking distinct keyword letters first and appending unused letters.

Choose the text, counts, explicit reference time or format parameters requested by this tool. Follow the stated byte, epoch-time and randomness assumptions.

How to use Keyword Alphabet Builder and understand its results

Choose the text, counts, explicit reference time or format parameters requested by this tool. Follow the stated byte, epoch-time and randomness assumptions.
Enter keyword using the field table and calculation rules, then run the tool.
Read alphabet. The explanation below defines the units, signs, ordering and any flags or placeholder values.
If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.

Input field	Meaning	Value type; see rules below	Requirement
keyword	ASCII letter keyword	string; maximum length: 10000	Required

Enter an ASCII-letter-only keyword, which may be empty. The tool uppercases it, appends ABCDEFGHIJKLMNOPQRSTUVWXYZ and preserves only the first occurrence of each letter. The resulting alphabet contains each A–Z letter exactly once. An empty keyword produces the ordinary alphabet; punctuation, spaces and non-ASCII letters are input errors.

alphabet = first-occurrence unique letters of uppercase(keyword) + A…Z

Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.

Output field	Meaning	Value type
alphabet	Keyword substitution alphabet	string

json

{
  "input": {
    "keyword": "BANANA"
  },
  "output": {
    "alphabet": "BANCDEFGHIJKLMOPQRSTUVWXYZ"
  }
}

Limitations and assumptions

This constructs a classical substitution alphabet without encrypting or decrypting a message. It does not preserve case or support other character sets, and a keyword alphabet does not provide the security properties of modern cryptography.

Numeric inputs must be finite. Follow the calculation-specific rules for overflow, underflow and exceptional cases. Extremely large text inputs are rejected. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.

Alternative or Complementary methods

Use Index of Coincidence Calculator: Calculate the probability that two letters drawn without replacement match, using only ASCII A–Z letters from the supplied text. For a complementary task, use Null Cipher Nth-Letter Extractor: Extract every nth Unicode code point at a one-based starting offset from an explicit text stream, including whitespace.

References

Keyword Alphabet Builder — tool.io

Similar or alternative tools

Index of Coincidence Calculator
Calculate the probability that two letters drawn without replacement match, using only ASCII A–Z letters from the supplied text.
Null Cipher Nth-Letter Extractor
Extract every nth Unicode code point at a one-based starting offset from an explicit text stream, including whitespace.