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Add sample encrypt-to-TPM scripts
This commit is contained in:
parent
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4 changed files with 456 additions and 4 deletions
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@ -1,6 +1,7 @@
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# What Attestation is
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A computer can use a TPM to demonstrate:
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An [enrolled device](/Enrollment/README.md) can use a TPM to
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demonstrate:
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- possession of a valid TPM
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@ -820,6 +821,11 @@ We'll discuss two ways to do this:
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the value zero so that extending it can disable use of
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`TPM2_MakeCredential()` post-boot.
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We have two sample bash scripts demonstrating this approach:
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- [`send-to-tpm.sh`](/Enrollment/send-to-tpm.sh)
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- [`tpm-receive.sh`](/Enrollment/tpm-receive.sh)
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- use an `LTAK` -- a long-term `AK`
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I.e., an `AK` that lacks the `stClear` attribute, and _preferably_
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@ -38,7 +38,7 @@ device using only that information.
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- encrypted filesystems?
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- device credentials? (e.g., TLS server certificates, Kerberos keys ["keytabs"], etc.)
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# Secrets Transport
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# Secrets Long-Term Storage and Transport
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Every time an enrolled device reboots, or possibly more often, it may
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have to connect to an attestation server to obtain secrets from it that
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@ -46,8 +46,95 @@ the device needs in order to proceed. For example, filesystem
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decryption keys, general network access, device authentication
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credentials, etc.
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See [attestation](/Attestation/README.md) for details of how to
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transport secrets onto an enrolled device post-enrollment.
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See [attestation](/Attestation/README.md#Secret-Transport-Sub-Protocols)
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for details of how to store and transport secrets onto an enrolled
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device post-enrollment.
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## Encrypt-to-TPM Sample Scripts
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A pair of scripts are included here to demonstrate how to make long-term
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secrets encrypted to TPMs for use in
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[attestation](/Attestation/README.md) protocols. The method used is the
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one described in the [attestation
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tutorial](/Attestation/README.md#Secret-Transport-Sub-Protocols) using
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[`TPM2_MakeCredential()`](/TPM-Commands/TPM2_MakeCredential.md) and
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[`TPM2_ActivateCredential()`](/TPM-Commands/TPM2_ActivateCredential.md)
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with a hard-coded, _well-known_ activation key (`WK`) to implement
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encryption-to-`EKpub` with (optional) sender-asserted authorization
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policy:
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- [`send-to-tpm.sh`](send-to-tpm.sh)
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- [`tpm-receive.sh`](tpm-receive.sh)
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You can use these scripts like so:
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- without policy:
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```bash
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: ; # Make a secret
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: ; dd if=/dev/urandom of=secret.bin bs=16 count=1
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: ;
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: ; # Encrypt the secret to some TPM whose EKpub is in a file named
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: ; # ek.pub:
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: ; /safeboot/sbin/send-to-tpm.sh ek.pub secret.bin cipher.bin
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fd32fa22c52cfc8e1a0c29eb38519f87084cab0b04b0d8f020a4d38b2f4e223e
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7fdad037a921f7eec4f97c08722692028e96888f0b970dc7b3bb6a9c97e8f988
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```
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```bash
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: ; # Decrypt the secret:
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: ; tpm-receive.sh cipher.bin secret.bin
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fd32fa22c52cfc8e1a0c29eb38519f87084cab0b04b0d8f020a4d38b2f4e223e
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7fdad037a921f7eec4f97c08722692028e96888f0b970dc7b3bb6a9c97e8f988
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name: 000be1fe1b777ead331f2da896ced2bf7a3949d732a0c6adf6f0a292567d587c4408
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837197674484b3f81a90cc8d46a5d724fd52d76e06520b64f2a1da1b331469aa
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fd32fa22c52cfc8e1a0c29eb38519f87084cab0b04b0d8f020a4d38b2f4e223e
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7fdad037a921f7eec4f97c08722692028e96888f0b970dc7b3bb6a9c97e8f988
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certinfodata:b7bd59980628c33a14377d53e165c229
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: ;
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- with policy
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```bash
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: ; # Make up a policy (here that PCR11 must be unextended):
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: ; dd if=/dev/zero of=pcr.dat bs=32 count=1
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: ; policy=(tpm2 policypcr -l sha256:11 -f pcr.dat)
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: ;
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: ; send-to-tpm.sh ek.pub secret.bin cipher.bin "${policy[@]}"
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fd32fa22c52cfc8e1a0c29eb38519f87084cab0b04b0d8f020a4d38b2f4e223e
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7fdad037a921f7eec4f97c08722692028e96888f0b970dc7b3bb6a9c97e8f988
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```
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```bash
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: ; # We have to satisfy the same policy on the receive side:
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: ; policy=(tpm2 policypcr -l sha256:11 -f pcr.dat)
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: ;
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: ; tpm-receive.sh -f cipher.bin "${policy[@]}"
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fd32fa22c52cfc8e1a0c29eb38519f87084cab0b04b0d8f020a4d38b2f4e223e
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7fdad037a921f7eec4f97c08722692028e96888f0b970dc7b3bb6a9c97e8f988
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name: 000be1fe1b777ead331f2da896ced2bf7a3949d732a0c6adf6f0a292567d587c4408
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837197674484b3f81a90cc8d46a5d724fd52d76e06520b64f2a1da1b331469aa
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fd32fa22c52cfc8e1a0c29eb38519f87084cab0b04b0d8f020a4d38b2f4e223e
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7fdad037a921f7eec4f97c08722692028e96888f0b970dc7b3bb6a9c97e8f988
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certinfodata:b7bd59980628c33a14377d53e165c229
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: ;
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```
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Multiple policy commands can be separated with a quoted semi-colon:
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```bash
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send-to-tpm.sh ... tpm2 policyblah ... \; policyfoo ...
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```
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Multiple policy commands can be separated with a quoted semi-colon:
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```bash
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send-to-tpm.sh ... tpm2 policyblah ... \; policyfoo ...
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```
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When a policy is specified, these scripts will automatically set the
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`adminWithPolicy` attribute of the activation object, and will add
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`tpm2 policycommandcode TPM2_CC_ActivateCredential` to the policy, as
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that is required for activation objects with `adminWithPolicy` set.
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# Enrollment Semantics
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165
Enrollment/send-to-tpm.sh
Executable file
165
Enrollment/send-to-tpm.sh
Executable file
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#!/bin/bash
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PROG=${0##*/}
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set -euo pipefail
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function usage {
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((${1:-1} > 0)) && exec 1>&2
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cat <<EOF
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Usage: $PROG EK-PUB-FILE SECRET-FILE OUT-FILE
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$PROG EK-PUB-FILE SECRET-FILE OUT-FILE [POLICY-CMD [ARGS [\\; ...]]]
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$PROG -P well-known-key-name EK-PUB-FILE SECRET-FILE OUT-FILE
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Encrypts a small secret to a TPM's EKpub with the caller's choice of
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policy.
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Policies should be specified as a sequence of {tpm2 policy...}
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commands, with all necessary arguments except for {--session}|{-S}
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and {--policy}|{-L} options. Also, no need to include {tpm2
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policycommandcode}, as that will get added. E.g.:
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$ $PROG ./ekpub ./secret ./madecredential \\
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tpm2 policypcr -l "sha256:0,1,2,3" -f pcrs
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Options:
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-h This help message.
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-P WKname Use the given cryptographic name binding a policy for
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recipient to meet.
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-f Overwrite OUT-FILE.
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-x Trace this script.
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EOF
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exit ${1:-1}
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}
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force=false
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wkname=
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while getopts +:hfxP: opt; do
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case "$opt" in
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P) wkname=$OPTARG;;
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h) usage 0;;
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f) force=true;;
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x) set -vx;;
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*) usage;;
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esac
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done
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shift $((OPTIND - 1))
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(($# >= 3)) || usage
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ekpub_file=$1
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secret_file=$2
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out_file=$3
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shift 3
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function err {
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echo "ERROR: $*" 1>&2
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exit 1
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}
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[[ -f ${ekpub_file:-} ]] || usage
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[[ -f ${secret_file:-} ]] || usage
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[[ -f ${out_file:-} ]] && $force && rm -f "${out_file:-}"
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[[ -f ${out_file:-} ]] && err "output file ($out_file) exists"
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# Make a temp dir and remove it when we exit:
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d=
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trap 'rm -rf "$d"' EXIT
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d=$(mktemp -d)
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function exec_policy {
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local add_commandcode=true
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local has_policy=false
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while (($# > 0)); do
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has_policy=true
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cmd=()
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while (($# > 0)) && [[ $1 != ';' ]]; do
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cmd+=("$1")
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if ((${#cmd[@]} == 1)) && [[ ${cmd[0]} = tpm2_* ]]; then
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cmd+=(--session "${d}/session.ctx" --policy "${d}/policy")
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elif ((${#cmd[@]} == 2)) && [[ ${cmd[0]} = tpm2 ]]; then
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cmd+=(--session "${d}/session.ctx" --policy "${d}/policy")
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fi
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shift
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done
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(($# > 0)) && shift
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# Run the policy command in the temp dir. It -or the last command- must
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# leave a file there named 'policy'.
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"${cmd[@]}"
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if [[ ${cmd[0]} = tpm2 ]] && ((${#cmd[@]} == 1)); then
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echo "Policy is incomplete" 1>&2
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exit 1
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fi
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[[ ${cmd[0]} = tpm2 && ${cmd[1]} = policycommandcode ]] &&
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add_commandcode=false
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[[ ${cmd[0]} = tpm2_policycommandcode ]] && add_commandcode=false
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done
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$has_policy && $add_commandcode &&
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tpm2 policycommandcode --session "${d}/session.ctx" \
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--policy "${d}/policy" \
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TPM2_CC_ActivateCredential
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}
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function make_policyDigest {
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# Start a trial session, execute the given policy commands, save the
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# policyDigest.
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tpm2 startauthsession --session "${d}/session.ctx"
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exec_policy "$@"
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}
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function wkname {
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local attrs='decrypt|sign'
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local has_policy
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# This is the WK. It was generated with:
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# openssl genpkey -genparam \
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# -algorithm EC \
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# -out "${d}/ecp.pem" \
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# -pkeyopt ec_paramgen_curve:secp384r1 \
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# -pkeyopt ec_param_enc:named_curve
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# openssl genpkey -paramfile "${d}/ecp.pem"
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cat > "${d}/wkpriv.pem" <<EOF
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-----BEGIN PRIVATE KEY-----
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MIG2AgEAMBAGByqGSM49AgEGBSuBBAAiBIGeMIGbAgEBBDAlMnCWue7CfXjNLibH
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PTJrsOLUcoxqU3FLWYEWMI+HuPnzcwwl7SkKN6cpf4H3oQihZANiAAQ1pw6D5QVw
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vymljYVDyrUriOet8zPB/9tq9XJ7A54qsVkaVufAuEJ6GIvD4xUZ27manMosJADS
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aW2TLJkwxecRh2eTwPtSx2U32M2/yHeuWRV/0juiIozefPsTAlHAi3E=
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-----END PRIVATE KEY-----
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EOF
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tpm2 flushcontext --transient-object
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tpm2 flushcontext --loaded-session
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tpm2 flushcontext --saved-session 1>&2
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# Load
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attrs='decrypt|sign'
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if (($# > 0)); then
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make_policyDigest "$@" 1>&2
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attrs='adminwithpolicy|decrypt|sign'
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has_policy=true
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# Flush again, but this time not saved sessions
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tpm2 flushcontext --transient-object 1>&2
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tpm2 flushcontext --loaded-session 1>&2
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fi
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# Load the WK
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tpm2 loadexternal -C n \
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-Gecc \
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-r "${d}/wkpriv.pem" \
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${has_policy:+-L "${d}/policy"} \
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-a "$attrs" \
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-c "${d}/wk.ctx" |
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grep ^name: | cut -d' ' -f2
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}
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[[ -z $wkname ]] && wkname=$(wkname "$@")
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tpm2 makecredential \
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--tcti "none" \
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--encryption-key "${ekpub_file}" \
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--name "$wkname" \
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--secret "${secret_file}" \
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--credential-blob "$out_file"
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194
Enrollment/tpm-receive.sh
Executable file
194
Enrollment/tpm-receive.sh
Executable file
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#!/bin/bash
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PROG=${0##*/}
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set -euo pipefail
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function usage {
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echo "Usage: $PROG [OPTIONS] CIPHERTEXT-FILE OUT-FILE [POLICY-CMD [ARGS] [\; ...]]"
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cat <<EOF
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Usage: $PROG CIPHERTEXT-FILE OUT-FILE [POLICY-CMD [ARGS] [;] ...]
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"Activates" (decrypts) CIPHERTEXT-FILE made with TPM2_MakeCredential and
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writes the plaintext to OUT-FILE. If the sender asserted some policy,
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that policy must be repeated when invoking this program to decrypt the
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secret.
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Policies should be specified as a sequence of {tpm2 policy...}
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commands, with all necessary arguments except for {--session}|{-S}
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and {--policy}|{-L} options. Also, no need to include {tpm2
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policycommandcode}, as that will get added. E.g.:
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$ $PROG ./ekpub ./secret ./madecredential \\
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tpm2 policypcr -l "sha256:0,1,2,3" -f pcrs
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Options:
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-h This help message.
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-f Overwrite OUT-FILE.
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-x Trace this script.
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EOF
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exit 1
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}
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force=false
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verbose=false
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while getopts +:hfvx opt; do
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case "$opt" in
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h) usage 0;;
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f) force=true;;
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v) verbose=true;;
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x) set -vx;;
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*) usage;;
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esac
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done
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shift $((OPTIND - 1))
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(($# >= 2)) || usage
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ciphertext_file=$1
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out_file=$2
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shift 2
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[[ -f ${ciphertext_file:-} ]] || usage
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[[ -f ${out_file:-} ]] && $force && rm -f "$out_file"
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[[ -f ${out_file:-} ]] && usage
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d=
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trap 'rm -rf "$d"' EXIT
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d=$(mktemp -d)
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function v {
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if $verbose; then
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printf 'Running:'
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printf ' %q' "$@"
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printf '\n'
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fi >/dev/tty || true
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if "$@"; then
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$verbose && printf '(SUCCESS)\n' >/dev/tty || true
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else
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stat=$?
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printf 'ERROR: Command exited with %d\n' $stat >/dev/tty || true
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return $stat
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fi
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}
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function exec_policy {
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local add_commandcode=true
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local has_policy=false
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while (($# > 0)); do
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has_policy=true
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cmd=()
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while (($# > 0)) && [[ $1 != ';' ]]; do
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cmd+=("$1")
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if ((${#cmd[@]} == 1)) && [[ ${cmd[0]} = tpm2_* ]]; then
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cmd+=(--session "${d}/session.ctx" --policy "${d}/policy")
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elif ((${#cmd[@]} == 2)) && [[ ${cmd[0]} = tpm2 ]]; then
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cmd+=(--session "${d}/session.ctx" --policy "${d}/policy")
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fi
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shift
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done
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(($# > 0)) && shift
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# Run the policy command in the temp dir. It -or the last command- must
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# leave a file there named 'policy'.
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"${cmd[@]}"
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if [[ ${cmd[0]} = tpm2 ]] && ((${#cmd[@]} == 1)); then
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echo "Policy is incomplete" 1>&2
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exit 1
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fi
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[[ ${cmd[0]} = tpm2 && ${cmd[1]} = policycommandcode ]] &&
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add_commandcode=false
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[[ ${cmd[0]} = tpm2_policycommandcode ]] && add_commandcode=false
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done
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$has_policy && $add_commandcode &&
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tpm2 policycommandcode --session "${d}/session.ctx" \
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--policy "${d}/policy" \
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TPM2_CC_ActivateCredential
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}
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function make_policyDigest {
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tpm2 flushcontext --transient-object
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tpm2 flushcontext --loaded-session
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v tpm2 startauthsession --session "${d}/session.ctx"
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exec_policy "$@"
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}
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# Get the EK handle:
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tpm2 flushcontext --transient-object
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tpm2 flushcontext --loaded-session
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tpm2 flushcontext --saved-session 1>&2
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tpm2 createek --key-algorithm rsa \
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--ek-context "${d}/ek.ctx" \
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--public "${d}/ek.pub"
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# Make policyDigest and load WK
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attrs='decrypt|sign'
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adminwithpolicy=
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if (($# > 0)); then
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make_policyDigest "$@"
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attrs='adminwithpolicy|decrypt|sign'
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adminwithpolicy=true
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fi
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rm -f "${d}/session.ctx"
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# This is the WK. It was generated with:
|
||||
# openssl genpkey -genparam \
|
||||
# -algorithm EC \
|
||||
# -out "${d}/ecp.pem" \
|
||||
# -pkeyopt ec_paramgen_curve:secp384r1 \
|
||||
# -pkeyopt ec_param_enc:named_curve
|
||||
# openssl genpkey -paramfile "${d}/ecp.pem"
|
||||
cat > "${d}/wkpriv.pem" <<EOF
|
||||
-----BEGIN PRIVATE KEY-----
|
||||
MIG2AgEAMBAGByqGSM49AgEGBSuBBAAiBIGeMIGbAgEBBDAlMnCWue7CfXjNLibH
|
||||
PTJrsOLUcoxqU3FLWYEWMI+HuPnzcwwl7SkKN6cpf4H3oQihZANiAAQ1pw6D5QVw
|
||||
vymljYVDyrUriOet8zPB/9tq9XJ7A54qsVkaVufAuEJ6GIvD4xUZ27manMosJADS
|
||||
aW2TLJkwxecRh2eTwPtSx2U32M2/yHeuWRV/0juiIozefPsTAlHAi3E=
|
||||
-----END PRIVATE KEY-----
|
||||
EOF
|
||||
|
||||
# Load the WK
|
||||
v tpm2 flushcontext --transient-object 1>&2
|
||||
v tpm2 flushcontext --loaded-session 1>&2
|
||||
if v tpm2 loadexternal -C n \
|
||||
-Gecc \
|
||||
-r "${d}/wkpriv.pem" \
|
||||
${adminwithpolicy:+-L "${d}/policy"} \
|
||||
-a "$attrs" \
|
||||
-c "${d}/wk.ctx" > "${d}/out" 2> "${d}/err"; then
|
||||
cat "${d}/out" 1>&2
|
||||
else
|
||||
stat=$?
|
||||
echo "ERROR: Failed to load WK:" 1>&2
|
||||
cat "${d}/out"
|
||||
cat "${d}/err" 1>&2
|
||||
exit $stat
|
||||
fi
|
||||
|
||||
# Create empty auth session for EK
|
||||
v tpm2 flushcontext --transient-object
|
||||
v tpm2 flushcontext --loaded-session
|
||||
v tpm2 startauthsession --session "${d}/sessionek.ctx" --policy-session
|
||||
v tpm2 policysecret --session "${d}/sessionek.ctx" --object-context endorsement
|
||||
|
||||
activatecredential_args=()
|
||||
if (($# > 0)); then
|
||||
activatecredential_args+=(--credentialedkey-auth session:"${d}/session.ctx")
|
||||
# Create auth session for the WK, since it has adminWithPolicy
|
||||
v tpm2 flushcontext --transient-object
|
||||
v tpm2 flushcontext --loaded-session
|
||||
v tpm2 startauthsession --session "${d}/session.ctx" --policy-session
|
||||
exec_policy "$@"
|
||||
v tpm2 flushcontext --transient-object
|
||||
v tpm2 flushcontext --loaded-session
|
||||
fi
|
||||
# Finally, ActivateCredential
|
||||
$verbose && tpm2 readpublic -c "${d}/wk.ctx" | grep name:
|
||||
v tpm2 activatecredential --credentialedkey-context "${d}/wk.ctx" \
|
||||
"${activatecredential_args[@]}" \
|
||||
--credentialkey-context "${d}/ek.ctx" \
|
||||
--credentialkey-auth session:"${d}/sessionek.ctx" \
|
||||
--credential-blob "$ciphertext_file" \
|
||||
-o "$out_file"
|
Loading…
Reference in a new issue