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.TH "sntrup" "3" "" "" ""
.hy
.SS NAME
.PP
sntrup - C API for the libntruprime implementation of the Streamlined
NTRU Prime cryptosystem
.SS SYNOPSIS
.PP
Using libntruprime:
.IP
.nf
\f[C]
#include <ntruprime.h>
\f[R]
.fi
.PP
Link with \f[V]-lntruprime\f[R].
.PP
Key generation (for, e.g., \f[V]sntrup1277\f[R]):
.IP
.nf
\f[C]
unsigned char pk[sntrup1277_PUBLICKEYBYTES];
unsigned char sk[sntrup1277_SECRETKEYBYTES];

sntrup1277_keypair(pk,sk);
\f[R]
.fi
.PP
Encapsulation (for, e.g., \f[V]sntrup1277\f[R]):
.IP
.nf
\f[C]
unsigned char ct[sntrup1277_CIPHERTEXTBYTES];
unsigned char k[sntrup1277_BYTES];
const unsigned char pk[sntrup1277_PUBLICKEYBYTES];

sntrup1277_enc(ct,k,pk);
\f[R]
.fi
.PP
Decapsulation (for, e.g., \f[V]sntrup1277\f[R]):
.IP
.nf
\f[C]
unsigned char k[sntrup1277_BYTES];
const unsigned char ct[sntrup1277_CIPHERTEXTBYTES];
const unsigned char sk[sntrup1277_SECRETKEYBYTES];

sntrup1277_dec(k,ct,sk);
\f[R]
.fi
.SS DESCRIPTION
.PP
libntruprime is an implementation of the Streamlined NTRU
Prime (https://ntruprime.cr.yp.to) cryptosystem.
The C API for libntruprime provides the following functions:
.IP
.nf
\f[C]
sntrup{653,761,857,953,1013,1277}_keypair
sntrup{653,761,857,953,1013,1277}_enc
sntrup{653,761,857,953,1013,1277}_dec
\f[R]
.fi
.PP
All of these functions follow the SUPERCOP API for
KEMs (https://bench.cr.yp.to/call-kem.html) except that
.IP \[bu] 2
the function names are libntruprime-specific instead of
\f[V]crypto_kem_*\f[R],
.IP \[bu] 2
message lengths are \f[V]long long\f[R] instead of
\f[V]unsigned long long\f[R], and
.IP \[bu] 2
the functions return \f[V]void\f[R] instead of \f[V]int\f[R].
.PP
The details below use \f[V]sntrup1277\f[R] as an example.
.SS KEY GENERATION
.PP
The \f[V]sntrup1277_keypair\f[R] function randomly generates Alice\[cq]s
secret key \f[V]sk[0]\f[R], \f[V]sk[1]\f[R], \&...,
\f[V]sk[sntrup1277_SECRETKEYBYTES-1]\f[R] and Alice\[cq]s corresponding
public key \f[V]pk[0]\f[R], \f[V]pk[1]\f[R], \&...,
\f[V]pk[sntrup1277_PUBLICKEYBYTES-1]\f[R].
.SS ENCAPSULATION
.PP
The \f[V]sntrup1277_enc\f[R] function randomly generates a ciphertext
\f[V]ct[0]\f[R], \f[V]ct[1]\f[R], \&...,
\f[V]ct[sntrup1277_CIPHERTEXTBYTES-1]\f[R] and the corresponding session
key \f[V]k[0]\f[R], \f[V]k[1]\f[R], \&...,
\f[V]k[sntrup1277_BYTES-1]\f[R] given Alice\[cq]s public key
\f[V]pk[0]\f[R], \f[V]pk[1]\f[R], \&...,
\f[V]pk[sntrup1277_PUBLICKEYBYTES-1]\f[R].
.SS DECAPSULATION
.PP
The \f[V]sntrup1277_dec\f[R] function, given Alice\[cq]s secret key
\f[V]sk[0]\f[R], \f[V]sk[1]\f[R], \&...,
\f[V]sk[sntrup1277_SECRETKEYBYTES-1]\f[R], computes the session key
\f[V]k[0]\f[R], \f[V]k[1]\f[R], \&..., \f[V]k[sntrup1277_BYTES-1]\f[R]
corresponding to a ciphertext \f[V]ct[0]\f[R], \f[V]ct[1]\f[R], \&...,
\f[V]ct[sntrup1277_CIPHERTEXTBYTES-1]\f[R] that was encapsulated to
Alice.
.SS SEE ALSO
.PP
\f[B]sntrup\f[R](1), \f[B]randombytes\f[R](3)