Ubuntu Manpage: fido2-assert — get/verify a FIDO2 assertion

NAME

       fido2-assert — get/verify a FIDO2 assertion

SYNOPSIS

       fido2-assert -G [-bdhpruvw] [-t option] [-i input_file] [-o output_file] device
       fido2-assert -V [-dhpv] [-i input_file] key_file [type]

DESCRIPTION

fido2-assert gets or verifies a FIDO2 assertion.

The input of fido2-assert is defined by the parameters of the assertion to be obtained/verified. See the
“INPUT FORMAT” section for details.

The output of fido2-assert is defined by the result of the selected operation. See the “OUTPUT FORMAT”
section for details.

If an assertion is successfully obtained or verified, fido2-assert exits 0. Otherwise, fido2-assert
exits 1.

The options are as follows:

-G Tells fido2-assert to obtain a new assertion from device.

-V Tells fido2-assert to verify an assertion using the PEM-encoded public key in key_file of type
type, where type may be es256 (denoting ECDSA over NIST P-256 with SHA-256), es384 (denoting
ECDSA over NIST P-384 with SHA-384), rs256 (denoting 2048-bit RSA with PKCS#1.5 padding and
SHA-256), or eddsa (denoting EDDSA over Curve25519 with SHA-512). If type is not specified,
es256 is assumed.

-b Request the credential's “largeBlobKey”, a 32-byte symmetric key associated with the asserted
credential.

-h If obtaining an assertion, enable the FIDO2 hmac-secret extension. If verifying an assertion,
check whether the extension data bit was signed by the authenticator.

-d Causes fido2-assert to emit debugging output on stderr.

-i input_file
Tells fido2-assert to read the parameters of the assertion from input_file instead of stdin.

-o output_file
Tells fido2-assert to write output on output_file instead of stdout.

-p If obtaining an assertion, request user presence. If verifying an assertion, check whether the
user presence bit was signed by the authenticator.

-r Obtain an assertion using a resident credential. If -r is specified, fido2-assert will not
expect a credential id in its input, and may output multiple assertions. Resident credentials
are called “discoverable credentials” in CTAP 2.1.

-t option
Toggles a key/value option, where option is a string of the form “key=value”. The options
supported at present are:

up=true|false
Asks the authenticator for user presence to be enabled or disabled.

uv=true|false
Asks the authenticator for user verification to be enabled or disabled.

pin=true|false
Tells fido2-assert whether to prompt for a PIN and request user verification.

The -t option may be specified multiple times.

-u Obtain an assertion using U2F. By default, fido2-assert will use FIDO2 if supported by the
authenticator, and fallback to U2F otherwise.

-v If obtaining an assertion, prompt the user for a PIN and request user verification from the
authenticator. If verifying an assertion, check whether the user verification bit was signed by
the authenticator.

-w Tells fido2-assert that the first line of input when obtaining an assertion shall be interpreted
as unhashed client data. This is required by Windows Hello, which calculates the client data
hash internally.

If a tty is available, fido2-assert will use it to obtain the PIN. Otherwise, stdin is used.

INPUT FORMAT

       The input of fido2-assert consists of base64 blobs and UTF-8  strings  separated  by  newline  characters
       ('\n').

       When obtaining an assertion, fido2-assert expects its input to consist of:

             1.   client data hash (base64 blob);
             2.   relying party id (UTF-8 string);
             3.   credential id, if credential not resident (base64 blob);
             4.   hmac salt, if the FIDO2 hmac-secret extension is enabled (base64 blob);

       When verifying an assertion, fido2-assert expects its input to consist of:

             1.   client data hash (base64 blob);
             2.   relying party id (UTF-8 string);
             3.   CBOR encoded authenticator data (base64 blob);
             4.   assertion signature (base64 blob);

       UTF-8 strings passed to fido2-assert must not contain embedded newline or NUL characters.

OUTPUT FORMAT

       The  output  of  fido2-assert  consists of base64 blobs and UTF-8 strings separated by newline characters
       ('\n').

       For each generated assertion, fido2-assert outputs:

             1.   client data hash (base64 blob);
             2.   relying party id (UTF-8 string);
             3.   CBOR encoded authenticator data (base64 blob);
             4.   assertion signature (base64 blob);
             5.   user id, if credential resident (base64 blob);
             6.   hmac secret, if the FIDO2 hmac-secret extension is enabled (base64 blob);
             7.   the credential's associated 32-byte  symmetric  key  (“largeBlobKey”),  if  requested  (base64
                  blob).

       When verifying an assertion, fido2-assert produces no output.

EXAMPLES