export function kdfCounterMode()

in modules/kdf-ctr-mode-node/src/kdfctr.ts [33:82]

• 40 lines of code
• 4 McCabe index (conditional complexity)

export function kdfCounterMode({
  digestAlgorithm,
  ikm,
  nonce,
  purpose,
  expectedLength,
}: KdfCtrInput): Buffer {
  /* Precondition: the ikm must be 32, 48, 66 bytes long */
  needs(
    SUPPORTED_IKM_LENGTHS.includes(ikm.length),
    `Unsupported IKM length ${ikm.length}`
  )
  /* Precondition: the nonce is required */
  needs(nonce, 'The nonce must be provided')
  /* Precondition: the nonce must be 16, 32 bytes long */
  needs(
    SUPPORTED_NONCE_LENGTHS.includes(nonce.length),
    `Unsupported nonce length ${nonce.length}`
  )
  /* Precondition: the expected length must be 32, 64 bytes */
  /* Precondition: the expected length * 8 must be under the max 32-bit signed integer */
  needs(
    SUPPORTED_DERIVED_KEY_LENGTHS.includes(expectedLength) &&
      expectedLength * 8 < INT32_MAX_LIMIT &&
      expectedLength * 8 > 0,
    `Unsupported requested length ${expectedLength}`
  )

  const label = purpose || Buffer.alloc(0)
  const info = nonce
  const internalLength = 8 + SEPARATION_INDICATOR.length

  /* Precondition: the input length must be under the max 32-bit signed integer */
  needs(
    internalLength + label.length + info.length < INT32_MAX_LIMIT,
    `Input Length ${
      internalLength + label.length + info.length
    } must be under ${INT32_MAX_LIMIT} bytes`
  )

  const lengthBits = Buffer.from(uInt32BE(expectedLength * 8))
  const explicitInfo = Buffer.concat([
    label,
    SEPARATION_INDICATOR,
    info,
    lengthBits,
  ])

  return rawDerive(ikm, explicitInfo, expectedLength, digestAlgorithm)
}