@Override
  public byte[] getKdfId() throws GeneralSecurityException {
    switch (macAlgorithm) {
      case "HmacSha256":
        return HpkeUtil.HKDF_SHA256_KDF_ID;
      case "HmacSha384":
        return HpkeUtil.HKDF_SHA384_KDF_ID;
      case "HmacSha512":
        return HpkeUtil.HKDF_SHA512_KDF_ID;
      default:
        throw new GeneralSecurityException("Could not determine HPKE KDF ID");
    }
  }
Copied from {@link com.google.crypto.tink.subtle.Hkdf#computeHkdf(String, byte[], byte[],
byte[], int)}
java_src/src/main/java/com/google/crypto/tink/hybrid/internal/HkdfHpkeKdf.java