FIDO_ASSERT_VERIFY(3) | Library Functions Manual | FIDO_ASSERT_VERIFY(3)

# NAME

`fido_assert_verify` — verifies the signature of a FIDO2 assertion statement

# SYNOPSIS

library “libfido2” libcbor libcrypto libz
`#include <fido.h>`

int
`fido_assert_verify`(const fido_assert_t *assert, size_t idx, int cose_alg, const void *pk);

# DESCRIPTION

The `fido_assert_verify`() function verifies whether the signature contained in statement index idx of assert matches the parameters of the assertion. Before using `fido_assert_verify`() in a sensitive context, the reader is strongly encouraged to make herself familiar with the FIDO2 assertion statement process as defined in the Web Authentication (webauthn) standard.

A brief description follows:

The `fido_assert_verify`() function verifies whether the client data hash, relying party ID, user presence and user verification attributes of assert have been attested by the holder of the private counterpart of the public key pk of COSE type cose_alg, where cose_alg is `COSE_ES256`, `COSE_RS256`, or `COSE_EDDSA`, and pk points to a es256_pk_t, rs256_pk_t, or eddsa_pk_t type accordingly.

Please note that the first statement in assert has an idx of 0.

# RETURN VALUES

The error codes returned by `fido_assert_verify`() are defined in `<fido/err.h>`. If statement idx of assert passes verification with pk, then `FIDO_OK` is returned.

# SEE ALSO

fido_assert_new(3), fido_assert_set_authdata(3)

July 9, 2025 | Debian