Merge remote-tracking branch 'cfvescovo/polybius' into add-tests-for-polybius-cipher

Author: task4233

ciphers/polybius.go

@@ -0,0 +1,59 @@
+package main
+
+import (
+	"errors"
+	"strings"
+)
+
+type polybius struct {
+	size       int
+	characters string
+	key        string
+}
+
+func newPolybius(key string, size int, chars string) (*polybius, error) {
+	key = strings.ToUpper(key)
+	chars = strings.ToUpper(chars)[:size]
+	if len(chars) != size {
+		return nil, errors.New("chars must be as long as size")
+	}
+	if len(key) != size*size {
+		return nil, errors.New("key must be as long as the size squared")
+	}
+	return &polybius{size, chars, key}, nil
+}
+
+func (p *polybius) encrypt(text string) string {
+	chars := []rune(strings.ToUpper(text))
+	encryptedText := ""
+	for _, char := range chars {
+		encryptedText += p.encipher(char)
+	}
+	return encryptedText
+}
+
+func (p *polybius) decrypt(text string) string {
+	chars := []rune(strings.ToUpper(text))
+	decryptedText := ""
+	for i := 0; i < len(chars); i += 2 {
+		decryptedText += p.decipher(chars[i : i+2])
+	}
+	return decryptedText
+}
+
+func (p *polybius) encipher(char rune) string {
+	index := strings.IndexRune(p.key, char)
+	row := index / p.size
+	col := index % p.size
+	chars := []rune(p.characters)
+	return string([]rune{chars[row], chars[col]})
+}
+
+func (p *polybius) decipher(chars []rune) string {
+	if len(chars) != 2 {
+		panic("decipher takes two chars")
+	}
+	row := strings.IndexRune(p.characters, chars[0])
+	col := strings.IndexRune(p.characters, chars[1])
+	return string([]rune(p.key)[row*p.size+col])
+}