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KEYCTL_DH_COMPUTE(3)      Linux Key Management Calls      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  pub-
       lic 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)
Linux                             07 Apr 2016             KEYCTL_DH_COMPUTE(3)