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KEYCTL_PKEY_SIGN(3) Linux Public-Key Signatures KEYCTL_PKEY_SIGN(3)


keyctl_pkey_sign, keyctl_pkey_verify - Generate and verify signatures


#include <keyutils.h>

long keyctl_pkey_sign(key_serial_t key, const char *info,
                      const void *data, size_t data_len,
                      void *sig, size_t sig_len);

long keyctl_pkey_verify(key_serial_t key, const char *info,
                        const void *data, size_t data_len,
                        const void *sig, size_t sig_len);


keyctl_pkey_sign() asks the kernel to use the crypto data attached to a key to generate a detached signature for a blob of data. Note that this may involve calling out to cryptographic hardware.

keyctl_pkey_verify() asks the kernel to use the key to generate a verify the signature against the same blob of data. This may also involve calling out to cryptographic hardware.

The caller must have search permission on a key to be able to perform either operation.

When invoking the function, key indicates the key that will provide the cryptographic material and info points to a comma-separated string of "key[=value]" parameters that indicate things like encoding forms and passwords to unlock the key; see asymmetric-key(7) for more information.

data and datalen indicate the address and size of the buffer of data to be signed and sig and siglen indicate the address and size of the signature buffer. The sign function draws data from the data buffer, generates a signature from it and places the output into the signature buffer. The verify function also draws data from the data buffer, then decrypts the signature and compares the result.

Note that the data buffer is strictly limited in capacity, typically unable to hold more bits than the size of the key. The caller is expected to have pre-digested the actual data and will thus pass the digest output to this function. The name of the digest used should be passed as part of the info string as hash=<name> for use in constructing the signature metadata.

keyctl_pkey_query(2) can be called to find out how large the buffers need to be and what the maximum size of the data can be for a specific signature encoding.

Note that not all asymmetric-type keys will support these operations; further, the operations available may depend on which components of the key material are available: typically encryption only requires the public key, but decryption requires the private key as well. Which operations are supported on a particular key can also be determined using the query function.


On success keyctl_pkey_sign() returns the amount of data written into the signature buffer. keyctl_pkey_verify() will return 0 in this case as it doesn't write to userspace.

On error the value -1 will be returned and errno will have been set to an appropriate error.


The key specified is invalid.
The key specified has expired.
The key specified has been revoked.
The key exists, but is not searchable by the calling process.
Some part of the key material or signature data is bad.
Signature verification failed.
Some facility needed to complete the requested operation is not available. This is most probably a requested or required digest or encryption algorithm.
Bad address.


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


keyctl(1), add_key(2), keyctl(2), keyctl(3), keyctl_pkey_query(3), keyrings(7), keyutils(7)

8 Nov 2018 Linux