tpm2-totp(1)

General Commands Manual

tpm2-totp(1)

NAME

tpm2-totp(1) – generate or calculate TPM based TOTPs

SYNOPSIS

tpm2-totp [options]

DESCRIPTION

tpm2-totp creates a key inside a TPM 2.0 that can be used to generate time-based onetime passwords (TOTPs) to demonstrate to the user that a platform was not altered during his/her abscense and thus still trustworthy.

ARGUMENTS

The tpm2-totp command expects one of five command and provides a set of options.

COMMANDS

•: generate: Generate a new TOTP secret. Possible options: -b, -l, -N, -p, -P, -T
•: calculate: Calculate a TOTP value. Possible options: -N, -t, -T
•: reseal: Reseal TOTP secret to new PCRs, banks or values. Possible options: -b, -N, -p, -P (required), -T
•: recover: Recover the TOTP secret and display it again. Possible Options: -N, -P (required), -T
•: clean: Delete the consumed NV index. Possible Options: -N, -T

OPTIONS

•: -b <bank>[,<bank>[,...]], --banks <bank>[,<bank>[,...]]: Selected PCR banks (default: SHA1,SHA256)
•: -h, --help: Print help
•: -l, --label: Label to use for display in the TOTP authenticator app (default: TPM2-TOTP)
•: -N <nvindex>, --nvindex <nvindex>: TPM NV index to store data (default: 0x018094AF)
•: -p <pcr>[,<pcr>[,...]], --pcrs <pcr>[,<pcr>[,...]]: Selected PCR registers (default: 0,2,4,6)
•: -P <password>, --password <password>: Password for the secret (default: none) (commands: generate, recover, reseal)
•: -t, --time: Display the date/time of the TOTP calculation (commands: calculate)
•: -T <tcti-name>[:<tcti-config>], --tcti <tcti-name>[:<tcti-config>]: Select the TCTI to use. tcti-name is the name of the TCTI library. If present, the configuration string tcti-config is passed verbatim to the chosen TCTI library.

The TCTI can additionally be specified using the environment variable TPM2TOTP_TCTI. If both the command line option and the environment variable are present, the command line option is used.

If no TCTI is specified, the default TCTI configured on the system is used.

•: -v, --verbose: Print verbose messages

EXAMPLES

Setup

The TOTP secret can be generated with and without password. It is recommended to set a password -Pin order to enable recovery options. Also the PCRs and PCR banks can be selected -p and -b. Default values are PCRs 0,2,4 and banks SHA1, SHA256.

tpm2-totp generate
tpm2-totp -P verysecret generate
tpm2-totp -P verysecret -p 0,1,2,3,4,5,6 generate
tpm2-totp -p 0,1,2,3,4,5,6 -b SHA1,SHA256 generate

Boot

During boot the TOTP value for the current time, together with the current time should be shown to the user, e.g. using plymouth from mkinitrd or from dracut. The command to be executed is:

tpm2-totp calculate
tpm2-totp -t calculate

Recovery

In order to recover the QR code:

tpm2-totp -P verysecret recover

In order to reseal the secret:

tpm2-totp -P verysecret reseal
tpm2-totp -P verysecret -p 1,3,5,6 reseal

Deletion

In order to delete the created NV index:

tpm2-totp clean

NV index

All command additionally take the -N option to specify the NV index to be used. By default, 0x018094AF is used and recommended.

tpm2-totp -N 0x01800001 -P verysecret generate
tpm2-totp -N 0x01800001 calculate
tpm2-totp -N 0x01800001 -P verysecret recover
tpm2-totp -N 0x01800001 -P verysecret reseal

TCTI configuration

All commands take the -T option or the TPM2TOTP_TCTI environment variable to specify the TCTI to be used. If the TCTI is not specified explicitly, the default TCTI configured on the system is used. To e.g. use the TPM simulator bound to a given port, use

tpm2-totp -T mssim:port=2321 generate