private static SecretBytes getPrivateP521Value() {
    return SecretBytes.copyFrom(
        Hex.decode(
            "00FAD06DAA62BA3B25D2FB40133DA757205DE67F5BB0018FEE8C86E1B68C7E75C"
                + "AA896EB32F1F47C70855836A6D16FCC1466F6D8FBEC67DB89EC0C08B0E996B83"
                + "538"),
        InsecureSecretKeyAccess.get());
  }
Test vectors for HPKE. Generated by hand from the implementation here.
java_src/src/main/java/com/google/crypto/tink/hybrid/internal/testing/HpkeTestUtil.java