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 key
       keyctl_dh_compute_kdf - Derive key from a Diffie-Hellman shared

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 keyctl_dh_compute().

       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
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       bug report for this manual page, send it to  This page was obtained from the
       project's upstream Git repository
       on 2023-12-22.  (At that time, the date of the most recent commit
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       manual page), send a mail to

Linux                          07 Apr 2016          KEYCTL_DH_COMPUTE(3)

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