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
keyctl_dh_compute_kdf - Derive key from a Diffie-Hellman shared secret
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);
long keyctl_dh_compute_kdf(key_serial_t private, key_serial_t prime,
key_serial_t base, char *hashname, char *otherinfo,
size_t otherinfolen, char *buffer, size_t buflen);
DESCRIPTION
keyctl_dh_compute() computes a Diffie-Hellman public key or shared se-
cret. 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.
keyctl_dh_compute_kdf() derives a key from a Diffie-Hellman shared se-
cret according to the protocol specified in SP800-56A. The Diffie-Hell-
man computation is based on the same primitives as discussed for
keyctl_dh_compute().
To implement the protocol of SP800-56A base is a key containing the re-
mote public key to compute the Diffie-Hellman shared secret. That
shared secret is post-processed with a key derivation function.
The hashname specifies the Linux kernel crypto API name for a hash that
shall be used for the key derivation function, such as sha256. The
hashname must be a NULL terminated string. See /proc/crypto for avail-
able hashes on the system.
Following the specification of SP800-56A section 5.8.1.2 the otherinfo
parameter may be provided. The format of the OtherInfo field is defined
by the caller. The caller may also specify NULL as a valid argument
when no OtherInfo data shall be processed. The length of the otherinfo
parameter is specified with otherinfolen and is restricted to a maximum
length by the kernel.
The KDF returns the requested number of bytes specified with the genlen
or the buflen parameter depending on the invoked function.
buffer and buflen specify the buffer into which the computed result
will be placed.
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.
EMSGSIZE
When using keyctl_dh_compute_kdf(), the size of either otherin-
folen or buflen is too big.
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)
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