Method performEncode

src/Encoder/HMAC.js:58–93

* Performs encode on given content. * @protected * @param {Chain} content * @return {number[]|string|Uint8Array|Chain|Promise} Encoded content

(content)

   * @return {number[]|string|Uint8Array|Chain|Promise} Encoded content
   */
  async performEncode (content) {
    const message = content.getBytes()
    const algorithm = this.getSettingValue('algorithm')
    const blockSize = HashEncoder.getAlgorithmBlockSize(algorithm)

    // Shorten keys longer than block size by sending it through the hash func
    let key = this.getSettingValue('key')
    if (key.length > blockSize) {
      key = await this.createDigest(algorithm, key)
    }

    // Keys shorter than block size are padded to block size
    const outerKey = new Uint8Array(blockSize)
    outerKey.set(key, 0)

    // Compose inner message and prepare outer key
    const innerMessage = new Uint8Array(blockSize + message.length)
    innerMessage.set(outerKey, 0)
    innerMessage.set(message, blockSize)

    for (let i = 0; i < blockSize; i++) {
      innerMessage[i] ^= 0x36
      outerKey[i] ^= 0x5C
    }

    // Calculate inner digest
    const innerDigest = await this.createDigest(algorithm, innerMessage)

    // Compose outer message
    const outerMessage = new Uint8Array(blockSize + innerDigest.length)
    outerMessage.set(outerKey, 0)
    outerMessage.set(innerDigest, blockSize)

    // Calculate hmac digest
    return this.createDigest(algorithm, outerMessage)
  }

  /**
   * Creates message digest using given algorithm.