Static IV (ARCH5114)

Key go.security.static-iv · Severity error · Category security · CWE CWE-329

Using a constant or zero IV/nonce makes identical plaintexts under the same key produce identical ciphertext, destroying the semantic security of CBC/CTR/GCM.

Incorrect

func encrypt(block cipher.Block, plaintext []byte) []byte {
  iv := make([]byte, block.BlockSize()) // always zero
  stream := cipher.NewCTR(block, iv)
  out := make([]byte, len(plaintext))
  stream.XORKeyStream(out, plaintext)
  return out
}

Correct

func encrypt(block cipher.Block, plaintext []byte) ([]byte, error) {
  iv := make([]byte, block.BlockSize())
  if _, err := rand.Read(iv); err != nil {
    return nil, err
  }
  stream := cipher.NewCTR(block, iv)
  out := make([]byte, len(plaintext))
  stream.XORKeyStream(out, plaintext)
  return append(iv, out...), nil // prepend IV
}

Fix

Generate a unique, random IV/nonce with crypto/rand for every encryption and store it alongside the ciphertext.