---
name: "sntrup857_dec"
section: "3"
platform: "linux"
package: "libntruprime-dev"
version: "0~20241021-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/sntrup857_dec"
---

# sntrup857\_dec(3)

### NAME

sntrup - C API for the libntruprime implementation of the Streamlined NTRU Prime cryptosystem

### SYNOPSIS

Using libntruprime:

-

  ```
  #include <ntruprime.h>
  ```

Link with -lntruprime.

Key generation (for, e.g., sntrup1277):

-

  ```
  unsigned char pk[sntrup1277_PUBLICKEYBYTES];
  unsigned char sk[sntrup1277_SECRETKEYBYTES];
  sntrup1277_keypair(pk,sk);
  ```

Encapsulation (for, e.g., sntrup1277):

-

  ```
  unsigned char ct[sntrup1277_CIPHERTEXTBYTES];
  unsigned char k[sntrup1277_BYTES];
  const unsigned char pk[sntrup1277_PUBLICKEYBYTES];
  sntrup1277_enc(ct,k,pk);
  ```

Decapsulation (for, e.g., sntrup1277):

-

  ```
  unsigned char k[sntrup1277_BYTES];
  const unsigned char ct[sntrup1277_CIPHERTEXTBYTES];
  const unsigned char sk[sntrup1277_SECRETKEYBYTES];
  sntrup1277_dec(k,ct,sk);
  ```

### DESCRIPTION

libntruprime is an implementation of the Streamlined NTRU Prime (https://ntruprime.cr.yp.to) cryptosystem. The C API for libntruprime provides the following functions:

-

  ```
  sntrup{653,761,857,953,1013,1277}_keypair
  sntrup{653,761,857,953,1013,1277}_enc
  sntrup{653,761,857,953,1013,1277}_dec
  ```

All of these functions follow the SUPERCOP API for KEMs (https://bench.cr.yp.to/call-kem.html) except that

- •

  the function names are libntruprime-specific instead of crypto\_kem\_\*,

- •

  message lengths are long long instead of unsigned long long, and

- •

  the functions return void instead of int.

The details below use sntrup1277 as an example.

### KEY GENERATION

The sntrup1277\_keypair function randomly generates Alice’s secret key sk\[0\], sk\[1\], ..., sk\[sntrup1277\_SECRETKEYBYTES-1\] and Alice’s corresponding public key pk\[0\], pk\[1\], ..., pk\[sntrup1277\_PUBLICKEYBYTES-1\].

### ENCAPSULATION

The sntrup1277\_enc function randomly generates a ciphertext ct\[0\], ct\[1\], ..., ct\[sntrup1277\_CIPHERTEXTBYTES-1\] and the corresponding session key k\[0\], k\[1\], ..., k\[sntrup1277\_BYTES-1\] given Alice’s public key pk\[0\], pk\[1\], ..., pk\[sntrup1277\_PUBLICKEYBYTES-1\].

### DECAPSULATION

The sntrup1277\_dec function, given Alice’s secret key sk\[0\], sk\[1\], ..., sk\[sntrup1277\_SECRETKEYBYTES-1\], computes the session key k\[0\], k\[1\], ..., k\[sntrup1277\_BYTES-1\] corresponding to a ciphertext ct\[0\], ct\[1\], ..., ct\[sntrup1277\_CIPHERTEXTBYTES-1\] that was encapsulated to Alice.

### SEE ALSO

[**sntrup**(1)](/sntrup/1.md), [**randombytes**(3)](/randombytes/3.md)