# Re-encrypting decrypted plaintext throws OpenFHEException

**URL:** <https://openfhe.discourse.group/t/re-encrypting-decrypted-plaintext-throws-openfheexception/2082>\
**Category:** Library Questions\
**Created:** [July 2, 2025, 4:49pm UTC](https://openfhe.discourse.group/t/re-encrypting-decrypted-plaintext-throws-openfheexception/2082 "2025-07-02T16:49:57Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![faden](https://avatars.discourse-cdn.com/v4/letter/f/c68b51/32.png) [@faden](https://openfhe.discourse.group/u/faden)\
**Post date:** [July 2, 2025, 4:49pm UTC](https://openfhe.discourse.group/t/re-encrypting-decrypted-plaintext-throws-openfheexception/2082/1 "2025-07-02T16:49:57Z")

</div>

I am trying to run the following code, which tries to re-encrypt a decrypted plaintext, but it throws an OpenFHEException in a recursive call from the second `Encrypt`. Where am I going wrong?

```auto
#include <openfhe.h>

using namespace lbcrypto;

int main()
{
    CCParams<CryptoContextBGVRNS> params;
    params.SetPlaintextModulus(65537);

    CryptoContext<DCRTPoly> cc = GenCryptoContext(params);
    cc->Enable(PKE | LEVELEDSHE);

    KeyPair<DCRTPoly> kp = cc->KeyGen();

    std::vector<int64_t> vec(10, 1L);
    Plaintext plain = cc->MakePackedPlaintext(vec);
    Ciphertext<DCRTPoly> cipher = cc->Encrypt(kp.publicKey, plain);

    cc->Decrypt(kp.secretKey, cipher, &plain);
    cipher = cc->Encrypt(kp.publicKey, plain);
}

```

More specifically, I am getting the following exception:

```auto
terminate called after throwing an instance of 'lbcrypto::OpenFHEException'
  what(): openfhe-development/src/core/include/lattice/hal/default/dcrtpoly-impl.h:l.705:DropLastElements(): DropLastElements: Too few towers in input.

```

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<div class="post-metadata">

**Author:** ![ypolyakov](https://yyz1.discourse-cdn.com/flex031/user_avatar/openfhe.discourse.group/ypolyakov/32/47_2.png) [@ypolyakov](https://openfhe.discourse.group/u/ypolyakov)\
**Post date:** [July 9, 2025, 2:41am UTC](https://openfhe.discourse.group/t/re-encrypting-decrypted-plaintext-throws-openfheexception/2082/2 "2025-07-09T02:41:22Z")

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This is not the right (secure) way to use a plaintext. To encode a vector, `MakePackedPlaintext` should be used for an input vector (similar to how `plain` is generated). The `plain` plaintext in your code seems to be reused for the next plaintext (without calling any `MakePackedPlaintext` or an equivalent functionality). The plaintext that is populated by `Decrypt` automatically erases an instance of `DCRTPoly` so that it could not be used for any secret key recovery attack, i.e., extract the error from the decrypted polynomial.

You should instead use `plain->GetPackedValue()` to extract a vector of integers and encode it as a new plaintext by using `MakePackedPlaintext` before invoking the second `Encrypt`.