Porta Cipher Tool

Apply Porta explicit uppercase key convention. Classical educational encoding only; not secure encryption, no hidden normalization or inferred key.

Description

Porta substitution pairs key letters and swaps between alphabet halves.

Porta substitution pairs key letters and swaps between alphabet halves.^[1]

The reciprocal transformation is a historical cipher operation rather than modern secure encryption. Use Porta Cipher Tool to evaluate the supplied inputs under the specific model below.

When to use Porta Cipher Tool

Use Porta Cipher Tool to evaluate the supplied inputs under the specific model below. Choose the intended encoding, alphabet or check and keep the exact character, key and measurement conventions described below.

How to use Porta Cipher Tool and understand its results

Choose the intended encoding, alphabet or check and keep the exact character, key and measurement conventions described below.
Enter Text, Key using the field table and validation rules below, then run the tool.
Read Encoded and interpret units, signs, ordering and placeholders as explained below.
If the tool reports an input error, correct that field and rerun. A successful false result, empty match list or unknown-evidence placeholder has the specific meaning described here; check the limitations before applying the result.

Input field	Meaning	Value type	Requirement
text	Text	string	Required; constraints below
key	Key	string	Required; constraints below

Enter uppercase A–Z text and a nonempty uppercase key, each at most 4096 characters. Repeat the key and select its pair number floor(keyValue/2). Map A–M into N–Z with that offset and N–Z back into A–M with the inverse offset modulo 13. The operation is reciprocal and accepts empty text, with no automatic space removal or case conversion.

x<13→13+(x+floor(k/2)) mod 13; otherwise→(x−13−floor(k/2)) mod 13

Field order, units and branch conditions follow the implementation explanation above.

Output field	Meaning	Value type
encoded	Encoded	string

json

{
  "input": {
    "text": "ABC",
    "key": "ABC"
  },
  "output": {
    "encoded": "NOQ"
  }
}

Limitations and assumptions

The reciprocal transformation is a historical cipher operation rather than modern secure encryption. Apply the exact scope and assumptions described above.

All listed fields require explicit values. Unexpected fields, incorrect types, nonfinite numbers and sparse arrays fail validation. Domain-specific bounds, alignments and supported tokens are stated above; extremely large inputs or outputs can also be rejected. These errors differ from successful results such as false, no matches or unknown evidence.

This educational transformation or format check does not establish modern cryptographic confidentiality, authentication or key security.

Alternative or Complementary methods

Use Gronsfeld Cipher Tool for a related task: Gronsfeld substitution shifts letters using a repeated decimal-digit key.

Use Variant Beaufort Cipher Tool for a related task: Variant Beaufort subtracts repeated key letters from plaintext letter indices.

References

Porta Cipher Tool — tool.io

Similar or alternative tools

Gronsfeld Cipher Tool
Gronsfeld substitution shifts letters using a repeated decimal-digit key.
Variant Beaufort Cipher Tool
Variant Beaufort subtracts repeated key letters from plaintext letter indices.