KEYCTL_DH_COMPUTE(3)

NAME
keyctl_dh_compute - Compute a Diffie-Hellman shared secret or public key

SYNOPSIS
#include <keyutils.h>

long keyctl_dh_compute(key_serial_t private, key_serial_t prime,
key_serial_t base, char *buffer, size_t buflen);

long keyctl_dh_compute_alloc(key_serial_t private,
key_serial_t prime, key_serial_t base, void **_buffer);

DESCRIPTION
keyctl_dh_compute() computes a Diffie-Hellman public key or shared secret. That computation is:

    base ^ private ( mod prime )

When base is a key containing the shared generator value, the remote public key is computed. When base is a key containing the remote public key, the shared secret is computed.

base, private, and prime must all refer to user-type keys containing the parameters for the computation. Each of these keys must grant the caller read permission in order for them to be used.

buffer and buflen specify the buffer into which the computed result will be placed. buflen may be zero, in which case the buffer is not used and the minimum buffer length is fetched.

keyctl_dh_compute_alloc() is similar to keyctl_dh_compute() except that it allocates a buffer big enough to hold the payload data and places the data in it. If successful, a pointer to the buffer is placed in *_buffer. The caller must free the buffer.

RETURN VALUE
On success keyctl_dh_compute() returns the amount of data placed into the buffer when buflen is non-zero. When buflen is zero, the minimum buffer length to hold the data is returned.

On success keyctl_dh_compute_alloc() returns the amount of data in the buffer.

On error, both functions set errno to an appropriate code and return the value -1.

ERRORS

ENOKEY
    One of the keys specified is invalid or not readable.

EINVAL
    The buffer pointer is invalid or buflen is too small.

EOPNOTSUPP
    One of the keys was not a valid user key.

LINKING
This is a library function that can be found in libkeyutils. When linking, -lkeyutils should be specified to the linker.

SEE ALSO
keyctl(1),
keyctl(2),
keyctl(3),
keyutils(7)