crypto

Author: daviskamau

Diff for: learning_crypto/caesar_cipher.js

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+// Simplest form of cryptography
+// shift alphabetic letters by a number
+// ex: ABC -> DEF (shift by 3)
+
+const encrypt = (text, shift) => {
+  let cipher = ''
+  for (let i = 0; i < text.length; i++) {
+    let charCode = text.charCodeAt(i)
+    if (charCode === 32) {
+      cipher += ' '
+    } else {
+      if (charCode < 65 && charCode > 90) break
+      charCode = charCode + shift
+      if (charCode > 90) charCode = 64 + (charCode - 90)
+      cipher += String.fromCharCode(charCode)
+    }
+  }
+
+  return cipher
+}
+
+const decrypt = (cipher, shift) => {
+  let text = ''
+
+  for (let i = 0; i < cipher.length; i++) {
+    let charCode = cipher.charCodeAt(i)
+    if (charCode === 32) {
+      text += ' '
+    } else {
+      if (charCode < 65 && charCode > 90) break
+      charCode = charCode - shift
+      if (charCode < 65) charCode = 90 - (64 - charCode)
+      text += String.fromCharCode(charCode)
+    }
+  }
+
+  return text
+}
+
+
+module.exports = {
+  encrypt,
+  decrypt
+}

Diff for: learning_crypto/caesar_cipher.test.js

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+const caesor_sypher = require('./caesar_cipher')
+
+const shift = 3
+const text = 'HELLO WORLD'
+
+console.log(`Text: ${text}`)
+
+const cipher = caesor_sypher.encrypt(text, shift)
+console.log(`Cipher: ${cipher}`)
+
+const decrypted = caesor_sypher.decrypt(cypher, shift)
+console.log(`Decrypt: ${decrypted}`)

Diff for: learning_crypto/vigenere_cipher.js

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+// Improve caesar cipher cryptographic - vigenere cipher
+// Shifted by values defined by a key
+
+const SPACE_KEY = 32
+
+const isAlphabet = (value) => {
+  return value.split('').every((letter) => {
+    const charCode = letter.charCodeAt()
+    return charCode > 65 && charCode < 90
+  })
+}
+
+const encrypt = (text, key) => {
+  if (!isAlphabet(key)) return new Error('Key must be alphabet.')
+
+  let keyCursor = 0
+  let cipher = ''
+  for (let i = 0; i < text.length; i++) {
+    let charCode = text.charCodeAt(i)
+    if (charCode === SPACE_KEY) {
+      cipher += ' '
+      continue
+    }
+
+    if (charCode < 65 && charCode > 90) break
+
+    const keyCharCode = key.charCodeAt(keyCursor)
+    const shift = keyCharCode - 65
+    charCode = charCode + shift
+    if (charCode > 90) charCode = 64 + (charCode - 90)
+    cipher += String.fromCharCode(charCode)
+
+    keyCursor++
+    if (keyCursor === key.length) keyCursor = 0
+  }
+
+  return cipher
+}
+
+const decrypt = (cipher, key) => {
+  if (!isAlphabet(key)) return new Error('Key must be alphabet.')
+
+  let keyCursor = 0
+  let text = ''
+  for (let i = 0; i < cipher.length; i++) {
+    let charCode = cipher.charCodeAt(i)
+    if (charCode === SPACE_KEY) {
+      text += ' '
+      continue
+    }
+
+    if (charCode < 65 && charCode > 90) break
+
+    const keyCharCode = key.charCodeAt(keyCursor)
+    const shift = keyCharCode - 65
+    charCode = charCode - shift
+    if (charCode < 65) charCode = 90 - (64 - charCode)
+    
+    keyCursor++
+    if (keyCursor === key.length) keyCursor = 0
+    text += String.fromCharCode(charCode)
+  }
+
+  return text
+}
+
+module.exports = {
+  encrypt,
+  decrypt
+}

Diff for: learning_crypto/vigenere_cipher.test.js

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+const vigenere_cipher = require('./vigenere_cipher')
+
+const key = 'DUH'
+const text = 'THEY DRINK THE TEA'
+
+console.log(`Text: ${text}`)
+
+const cipher = vigenere_cipher.encrypt(text, key)
+console.log(`Cipher: ${cipher}`)
+
+const decrypt = vigenere_cipher.decrypt(cipher, key)
+console.log(`Decrypt: ${decrypt}`)