diff --git a/lib/utils/pkcs7-padding.js b/lib/utils/pkcs7-padding.js
index a2e52a41c..0b26a5264 100644
--- a/lib/utils/pkcs7-padding.js
+++ b/lib/utils/pkcs7-padding.js
@@ -1,42 +1,122 @@
 // @flow
 
+/**
+ * This file contains functions for PKCS#7 padding and unpadding, as well as
+ * functions for padding on the block basis. This is used to let the padding
+ * to be larger than maximum PKCS#7 padding block size (255 bytes).
+ *
+ * The main idea of this concept is to pad the input using the standard
+ * PKCS#7 padding, and then pad the result to the neares multiple of
+ * superblocks (blocks of blocks). The procedure is analogous
+ * to the standard PKCS#7 padding, but operates on the block basis instead of
+ * the byte basis. The fill value of the padding is the number of blocks added.
+ *
+ * The PKCS#7 padding is described in RFC 5652, section 6.3.
+ */
+
 import invariant from 'invariant';
 
 /**
  * PKCS#7 padding function for `Uint8Array` data.
  *
  * @param {Uint8Array} data - The data to be padded.
  * @param {number} blockSizeBytes - The block size in bytes.
  * @returns {Uint8Array} The padded data as a new Uint8Array.
  */
 function pkcs7pad(data: Uint8Array, blockSizeBytes: number): Uint8Array {
   invariant(blockSizeBytes > 0, 'block size must be positive');
   invariant(blockSizeBytes < 256, 'block size must be less than 256');
   const padding = blockSizeBytes - (data.length % blockSizeBytes);
   const padded = new Uint8Array(data.length + padding);
   padded.set(data);
   padded.fill(padding, data.length);
   return padded;
 }
 
 /**
  * PKCS#7 unpadding function for `Uint8Array` data.
  *
  * @param {Uint8Array} data - The padded data to be unpadded.
  * @returns {Uint8Array} The unpadded data as a new Uint8Array.
  * @throws {Error} If the padding is invalid.
  */
 function pkcs7unpad(data: Uint8Array): Uint8Array {
   const padding = data[data.length - 1];
   invariant(padding > 0, 'padding must be positive');
   invariant(data.length >= padding, 'data length must be at least padding');
   invariant(
     data.subarray(data.length - padding).every(x => x === padding),
     'invalid padding',
   );
 
   const unpadded = data.subarray(0, data.length - padding);
   return unpadded;
 }
 
-export { pkcs7pad, pkcs7unpad };
+/**
+ * Pads the PKCS#7-padded input on the block basis. Pads the input to have
+ * a length that is a multiple of the superblock size. The input must already
+ * be PKCS#7 padded to the block size.
+ *
+ * @param {Uint8Array} data - The PKCS#7 padded input to be block-padded.
+ * @param {number} blockSizeBytes - The block size in bytes.
+ * @param {number} superblockSize - The superblock size in blocks.
+ * @returns {Uint8Array} The block-padded data as a new Uint8Array.
+ */
+function superblockPad(
+  data: Uint8Array,
+  blockSizeBytes: number,
+  superblockSize: number,
+): Uint8Array {
+  invariant(
+    data.length % blockSizeBytes === 0,
+    'data length must be a multiple of block size',
+  );
+  invariant(superblockSize > 0, 'superblock size must be positive');
+  invariant(superblockSize <= 255, 'superblock size must be less than 256');
+  invariant(blockSizeBytes > 0, 'block size must be positive');
+  invariant(blockSizeBytes <= 255, 'block size must be less than 256');
+
+  const numBlocks = data.length / blockSizeBytes;
+  const paddingBlocks = superblockSize - (numBlocks % superblockSize);
+  const paddingValue = paddingBlocks;
+
+  const outputBuffer = new Uint8Array(
+    data.length + paddingBlocks * blockSizeBytes,
+  );
+  outputBuffer.set(data);
+  outputBuffer.fill(paddingValue, data.length);
+  return outputBuffer;
+}
+
+/**
+ * Unpads the block-padded input on the block basis.
+ *
+ * @param {Uint8Array} data  - The block-padded input to be unpaded.
+ * @param {number} blockSizeBytes - The block size in bytes.
+ * @returns {Uint8Array} - The unpadded data as a new Uint8Array.
+ */
+function superblockUnpad(data: Uint8Array, blockSizeBytes: number): Uint8Array {
+  invariant(blockSizeBytes > 0, 'block size must be positive');
+  invariant(blockSizeBytes <= 255, 'block size must be less than 256');
+  invariant(
+    data.length % blockSizeBytes === 0,
+    'data length must be a multiple of block size',
+  );
+
+  const numBlocks = data.length / blockSizeBytes;
+  const paddingBlocks = data[data.length - 1];
+  invariant(paddingBlocks > 0 && paddingBlocks < numBlocks, 'invalid padding');
+
+  const unpaddedBlocks = numBlocks - paddingBlocks;
+  const unpaddedLengthBytes = unpaddedBlocks * blockSizeBytes;
+  invariant(
+    data.subarray(unpaddedLengthBytes).every(x => x === paddingBlocks),
+    'invalid padding',
+  );
+
+  const unpaddedData = data.subarray(0, unpaddedLengthBytes);
+  return unpaddedData;
+}
+
+export { pkcs7pad, pkcs7unpad, superblockPad, superblockUnpad };
diff --git a/lib/utils/pkcs7-padding.test.js b/lib/utils/pkcs7-padding.test.js
index 562cdc43b..69cc3f188 100644
--- a/lib/utils/pkcs7-padding.test.js
+++ b/lib/utils/pkcs7-padding.test.js
@@ -1,89 +1,168 @@
 // @flow
 
-import { pkcs7pad, pkcs7unpad } from './pkcs7-padding.js';
+import {
+  pkcs7pad,
+  pkcs7unpad,
+  superblockPad,
+  superblockUnpad,
+} from './pkcs7-padding.js';
 
 describe('PKCS#7 Padding', () => {
   it('should pad data to a multiple of blockSize bytes', () => {
     const blockSize = 16;
     const data = generateRandomData(100);
     const expectedPadding = 16 - (data.length % blockSize);
 
     const padded = pkcs7pad(data, blockSize);
     expect(padded.length % 16).toBe(0);
     expect(padded[padded.length - 1]).toBe(expectedPadding);
   });
 
   it('pkcs7pad should add a full block if input is multiple of blockSize bytes', () => {
     const blockSize = 16;
     const data = generateRandomData(16);
     const expectedPadding = 16;
 
     const padded = pkcs7pad(data, blockSize);
     expect(padded.length % 16).toBe(0);
     expect(padded[padded.length - 1]).toBe(expectedPadding);
   });
 
   it('pkcs7pad should fail if blockSize is out of 1-255 range', () => {
     const data = generateRandomData(16);
     expect(() => pkcs7pad(data, 0)).toThrow();
     expect(() => pkcs7pad(data, 256)).toThrow();
   });
 
   it('pkcs7unpad should unpad data', () => {
     // blockSize = 16
     const inputData = generateRandomArray(10);
     const padded = new Uint8Array([...inputData, ...[6, 6, 6, 6, 6, 6]]);
 
     const unpadded = pkcs7unpad(padded);
     expect(unpadded.length).toBe(10);
     expect(unpadded).toStrictEqual(new Uint8Array(inputData));
   });
 
   it('pkcs7unpad should throw if the padding length is 0', () => {
     // blockSize = 16
     const padded = new Uint8Array([
       ...generateRandomArray(10),
       ...[0, 0, 0, 0, 0, 0],
     ]);
     expect(() => pkcs7unpad(padded)).toThrow();
   });
 
   it('pkcs7unpad should throw if the padding length is > blockSize', () => {
     // blockSize = 16
     const padded = new Uint8Array([
       ...generateRandomArray(10),
       ...[17, 17, 17, 17, 17, 17],
     ]);
     expect(() => pkcs7unpad(padded)).toThrow();
   });
 
   it('pkcs7unpad should throw if the padding is invalid', () => {
     // blockSize = 16
     const padded = new Uint8Array([
       ...generateRandomArray(10),
       ...[6, 1, 2, 3, 4, 6],
     ]);
     expect(() => pkcs7unpad(padded)).toThrow();
   });
 
   it('pkcs7pad and pkcs7unpad should be inverses', () => {
     const blockSize = 16;
     const data = generateRandomData(100);
     const padded = pkcs7pad(data, blockSize);
     const unpadded = pkcs7unpad(padded);
     expect(unpadded.length).toBe(data.length);
     expect(unpadded).toEqual(data);
   });
 });
 
+describe('superblock padding', () => {
+  it('should pad data to a multiple of superblockSize blocks', () => {
+    const blockSizeBytes = 16;
+    const superblockSizeBlocks = 4;
+    const dataLengthBytes = 3 * 16;
+    const expectedPaddedLength = 4 * 16;
+    const expectedBlockPadding = 1;
+
+    const data = generateRandomData(dataLengthBytes);
+    const padded = superblockPad(data, blockSizeBytes, superblockSizeBlocks);
+
+    expect(padded.length % expectedPaddedLength).toBe(0);
+    expect(padded[padded.length - 1]).toBe(expectedBlockPadding);
+  });
+
+  it('pad should add a full superblock if input is a multiple of superblockSize blocks', () => {
+    const blockSizeBytes = 16;
+    const superblockSizeBlocks = 4;
+    const dataLengthBytes = 4 * 16;
+    const expectedPaddedLength = 8 * 16;
+    const expectedBlockPadding = 4;
+
+    const data = generateRandomData(dataLengthBytes);
+    const padded = superblockPad(data, blockSizeBytes, superblockSizeBlocks);
+
+    expect(padded.length % expectedPaddedLength).toBe(0);
+    expect(padded[padded.length - 1]).toBe(expectedBlockPadding);
+  });
+
+  it('superblockUnpad should unpad data', () => {
+    const blockSizeBytes = 16;
+
+    // 2 blocks of data + 2 blocks of padding = 4 blocks total (1 superblock)
+    const padded = new Uint8Array([
+      ...generateRandomArray(2 * 16),
+      ...new Array(2 * 16).fill(2),
+    ]);
+
+    const unpadded = superblockUnpad(padded, blockSizeBytes);
+
+    expect(unpadded.length).toBe(32);
+    expect(unpadded).toEqual(padded.subarray(0, 32));
+  });
+
+  it('superblockUnpad should throw if the padding length is 0', () => {
+    const blockSizeBytes = 16;
+    const padded = new Uint8Array([
+      ...generateRandomArray(2 * 16),
+      ...new Array(2 * 16).fill(0),
+    ]);
+    expect(() => superblockUnpad(padded, blockSizeBytes)).toThrow();
+  });
+
+  it('superblockUnpad should throw if the padding length is > num blocks', () => {
+    const blockSizeBytes = 16;
+    // 4 blocks total, but filled with 5s
+    const padded = new Uint8Array([
+      ...generateRandomArray(2 * 16),
+      ...new Array(2 * 16).fill(5),
+    ]);
+    expect(() => superblockUnpad(padded, blockSizeBytes)).toThrow();
+  });
+
+  it('superblockUnpad should throw if the padding is invalid', () => {
+    const blockSizeBytes = 16;
+    const padded = new Uint8Array([
+      ...generateRandomArray(2 * 16),
+      ...generateRandomArray(2 * 15),
+      ...[1],
+    ]);
+    expect(() => superblockUnpad(padded, blockSizeBytes)).toThrow();
+  });
+});
+
 function generateRandomData(length: number): Uint8Array {
   const data = new Uint8Array(length);
   for (let i = 0; i < length; i++) {
     data[i] = Math.floor(Math.random() * 256);
   }
   return data;
 }
 
 function generateRandomArray(length: number): Array<number> {
   return new Array(length).map(() => Math.floor(Math.random() * 256));
 }