keyctl_dh_compute(3) — Linux manual page


KEYCTL_DH_COMPUTE(3)     Linux Key Management Calls     KEYCTL_DH_COMPUTE(3)

NAME         top

       keyctl_dh_compute  - Compute a Diffie-Hellman shared secret or public
       keyctl_dh_compute_kdf - Derive key from a Diffie-Hellman  shared  se‐

SYNOPSIS         top

       #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         top

       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.

       keyctl_dh_compute_kdf() derives a key from a Diffie-Hellman shared
       secret according to the protocol specified in SP800-56A. The Diffie-
       Hellman computation is based on the same primitives as discussed for

       To implement the protocol of SP800-56A base is a key containing the
       remote 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
       available hashes on the system.

       Following the specification of SP800-56A section 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         top

       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         top

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

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

              One of the keys was not a valid user key.

              When using keyctl_dh_compute_kdf(), the size of either
              otherinfolen or buflen is too big.

LINKING         top

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

SEE ALSO         top


COLOPHON         top

       This page is part of the keyutils (key management utilities) project.
       Information about the project can be found at [unknown -- if you
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       this manual page, send it to  This page was
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       on 2020-11-01.  (At that time, the date of the most recent commit
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       COLOPHON (which is not part of the original manual page), send a mail

Linux                            07 Apr 2016            KEYCTL_DH_COMPUTE(3)

Pages that refer to this page: keyctl(2)keyctl(3)