---

utils/preprocessPlaintextHex.ts

@@ -0,0 +1,49 @@
+import { PlaintextBlock} from './'
+
+export const preprocessPlaintextHex = (hexPlaintext: string): PlaintextBlock[] => {
+  /**
+   * @param {string} hexPlaintext - The plaintext to encrypt, as a hexadecimal string.
+   * @returns {PlaintextBlock[]} Blocks of 128 bits representing the plaintext. Each block is a 4x4 column-major matrix.
+   */
+  const blockSize = 16 // 128 bits = 16 bytes
+
+  // Convert the hex string into a byte array, where each pair of hex digits is a byte
+  const byteArray = new Uint8Array(hexPlaintext.match(/.{1,2}/g)!.map(byte => parseInt(byte, 16)))
+
+  // Loop through the byteArray and split it into 128-bit blocks
+  const blocks: Uint8Array[] = []
+  for (let i = 0;i < byteArray.length;i += blockSize) {
+    const block = byteArray.slice(i, i + blockSize)
+
+    if (block.length < blockSize) {
+      // Pad the block with zeroes
+      const paddedBlock = new Uint8Array(blockSize)
+      paddedBlock.set(block)
+      blocks.push(paddedBlock)
+    } else {
+      blocks.push(block)
+    }
+  }
+
+  const plaintextBlocks: number[][][] = blocks.map(block => {
+    // Block is a 128-bit array containing 16 8-bit integers.
+
+    const matrix: number[][] = [
+      [0, 0, 0, 0],
+      [0, 0, 0, 0],
+      [0, 0, 0, 0],
+      [0, 0, 0, 0],
+    ]
+
+    // Fill the matrix in column-major order, i.e., top-to-bottom + left-to-right
+    for (let i = 0;i < blockSize;i++) {
+      const row = i % 4
+      const col = Math.floor(i / 4)
+      matrix[row][col] = block[i]
+    }
+
+    return matrix
+  })
+
+  return plaintextBlocks
+}