tpm2_rsaencrypt(1)

📦
version 5.8 · 10 versions
, in arch rolling

💖 tpm2_rsaencrypt(1) — General Commands Manual, but make it cryptographic ✨

okay so bestie, welcome to tpm2_rsaencrypt(1), straight out of the General Commands Manual, and honestly this one is giving big "secret agent sending a sealed envelope" energy 🕵️♀️🎀

🎀 NAME 🎀

tpm2_rsaencrypt(1) — Performs an RSA encryption operation using the TPM. that's it, that's the whole thing, and she ate 💅

🌸 SYNOPSIS 🌸

tpm2_rsaencrypt [OPTIONS] [ARGUMENT]

🦋 DESCRIPTION 🦋

tpm2_rsaencrypt(1) — Performs RSA encryption on the contents of file data using the indicated padding scheme according to IETF RFC 3447 (PKCS#1). no cap, real standards-body behaviour 🫶 and if you don't specify input, it defaults to STDIN, so it's lowkey ready whenever you pipe something in.

the key that key-context points at has to be:

  1. An RSA key 🔑
  2. Have the attribute encrypt SET in it's attributes.

like, both. not one or the other. the vibe check is non-negotiable 😭

✨ OPTIONS ✨

  • -c, --key-context=OBJECT — Context object pointing to the the public portion of RSA key to use for encryption. (yes, "the the", she's a little quirky, we love her 💜)
  • -o, --output=FILE — Optional output file path to record the encrypted data to. the default is to print the binary encrypted data to stdout, so if you don't give her a file she's just gonna yeet binary into your terminal 🫠
  • -s, --scheme=FORMAT — Optional, set the padding scheme (defaults to rsaes). the options are:
    • null — TPM_ALG_NULL uses the key's scheme if set. iykyk, it defers to whatever the key already decided 🌈
    • rsaes — TPM_ALG_RSAES which is RSAES_PKCSV1.5. the default bestie fr fr
    • oaep — TPM_ALG_OAEP which is RSAES_OAEP. fancy padding, iconic behaviour ✨
  • -l, --label=FILE or STRING — Optional, set the label data. Can either be a string or file path. so here's the tea: the TPM requires the last byte of the label to be zero, this is handled internally to the tool. but no other embedded 0 bytes can exist or the TPM will truncate your label — that's a real one, don't get caught slipping 💀
  • ARGUMENT — the command line argument specifies the path of the file with data to be encrypted. that's your plaintext bestie, guard it 🎀

📚 References

Context Object Format

The type of a context object, whether it is a handle or file name, is determined according to the following logic in-order:

  • If the argument is a file path, then the file is loaded as a restored TPM transient object. 📂
  • If the argument is a prefix match on one of:
    • owner: the owner hierarchy
    • platform: the platform hierarchy
    • endorsement: the endorsement hierarchy
    • lockout: the lockout control persistent object
  • If the argument argument can be loaded as a number it will be treat as a handle, e.g. 0x81010013 and used directly._OBJECT_. 👑 (yes that _OBJECT_ is just sitting there at the end, we're not touching it, she's part of the family now)

🔐 Authorization Formatting

Authorization for use of an object in TPM2.0 can come in 3 different forms:

  1. Password
  2. HMAC
  3. Sessions
NOTE: "Authorizations default to the EMPTY PASSWORD when not specified". like, nobody gave her a password so she's just walking in 🙈

For authentication with auth values, the tool commands implicitly generate an HMAC session. Thus passwords are not transmitted unencrypted. This does not apply to passwords defined for objects. In this case, an HMAC session should be used (see tpm2_startauthsession(1)). important little distinction, ok? 💅

🔑 Passwords

Passwords are interpreted in the following forms below using prefix identifiers.

Note: By default passwords are assumed to be in the string form when they do not have a prefix.

String

A string password, specified by prefix str: or it's absence (raw string without prefix) is not interpreted, and is directly used for authorization. so plain and simple, no decoding, she takes it at face value 🫶

Examples

foobar
str:foobar

Hex-string

A hex-string password, specified by prefix hex: is converted from a hexidecimal form into a byte array form, thus allowing passwords with non-printable and/or terminal un-friendly characters. perfect for the chaotic passwords, we stan 🧚

Example

hex:1122334455667788

File

A file based password, specified be prefix file: should be the path of a file containing the password to be read by the tool or a - to use stdin. Storing passwords in files prevents information leakage, passwords passed as options can be read from the process list or common shell history features. so like, do that, keep your secrets secret 🔒✨

Examples

# to use stdin and be prompted
file:-

# to use a file from a path
file:path/to/password/file

# to echo a password via stdin:
echo foobar | tpm2_tool -p file:-

# to use a bash here-string via stdin:

tpm2_tool -p file:- <<< foobar

🎟️ Sessions

When using a policy session to authorize the use of an object, prefix the option argument with the session keyword. Then indicate a path to a session file that was created with tpm2_startauthsession(1). Optionally, if the session requires an auth value to be sent with the session handle (eg policy password), then append a + and a string as described in the Passwords section.

Examples

To use a session context file called session.ctx.

session:session.ctx

To use a session context file called session.ctx AND send the authvalue mypassword.

session:session.ctx+mypassword

To use a session context file called session.ctx AND send the HEX authvalue 0x11223344.

session:session.ctx+hex:11223344

🧬 PCR Authorizations

You can satisfy a PCR policy using the pcr: prefix and the PCR minilanguage. The PCR minilanguage is as follows:

<pcr-spec>=<raw-pcr-file>

The PCR spec is documented in the section "PCR bank specifiers".

The raw-pcr-file is an optional argument that contains the output of the raw PCR contents as returned by tpm2_pcrread(1).

PCR bank specifiers

(that's the section, bestie, and it's right here — no extra details hiding, promise 🌸)

Examples

To satisfy a PCR policy of sha256 on banks 0, 1, 2 and 3 use a specifier of:

pcr:sha256:0,1,2,3

specifying AUTH. 🫶

⚙️ COMMON OPTIONS

This collection of options are common to many programs and provide information that many users may expect. the little shared wardrobe of flags, if you will 👗

  • -h, --help=[man|no-man] — Display the tools manpage. By default, it attempts to invoke the manpager for the tool, however, on failure will output a short tool summary. This is the same behavior if the "man" option argument is specified, however if explicit "man" is requested, the tool will provide errors from man on stderr. If the "no-man" option if specified, or the manpager fails, the short options will be output to stdout.

To successfully use the manpages feature requires the manpages to be installed or on MANPATH, See man(1) for more details. 📖

  • -v, --version — Display version information for this tool, supported tctis and exit. quick little flex and dip ✌️
  • -V, --verbose — Increase the information that the tool prints to the console during its execution. When using this option the file and line number are printed. she gets chatty and specific 💬
  • -Q, --quiet — Silence normal tool output to stdout. 🤫
  • -Z, --enable-errata — Enable the application of errata fixups. Useful if an errata fixup needs to be applied to commands sent to the TPM. Defining the environment TPM2TOOLS_ENABLE_ERRATA is equivalent. 🔧
  • -z, --pwd-session — Use password session instead of a HMAC session for authentication. A clear text password is passed to the TPM to authorize the action. This option can be used to avoid problems when unsalted sessions are used in OpenSSL FIPS mode. If auth values are used a salted session should be used for authentication. ⚠️ like, clear text, ok, be aware of that
  • -R, --autoflush — Enable autoflush for transient objects created by the command. If a parent object is loaded from a context file also the transient parent object will be flushed. Autoflush can also be activated if the environment variable TPM2TOOLS_AUTOFLUSH is is set to yes or true. information many users may expect. 🧹 (and yes, "is is", she's doing her best)

🔌 TCTI Configuration

The TCTI or "Transmission Interface" is the communication mechanism with the TPM. TCTIs can be changed for communication with TPMs across different mediums. it's literally the phone line to your TPM 📞

To control the TCTI, the tools respect:

  1. The command line option -T or --tcti
  2. The environment variable: TPM2TOOLS_TCTI.

Note: The command line option always overrides the environment variable. no arguments, that's the rule 👑

The current known TCTIs are:

  • tabrmd — The resource manager, called tabrmd. Note that tabrmd and abrmd as a tcti name are synonymous. 🧠
  • mssim — Typically used for communicating to the TPM software simulator. 🖥️
  • device — Used when talking directly to a TPM device file. 🔩
  • none — Do not initalize a connection with the TPM. Some tools allow for off-tpm options and thus support not using a TCTI. Tools that do not support it will error when attempted to be used without a TCTI connection. Does not support ANY options and MUST BE presented as the exact text of none. so like, spell it exactly, no extra credit 🙅♀️

The arguments to either the command line option or the environment variable are in the form:

<tcti-name>:<tcti-option-config>

Specifying an empty string for either the <tcti-name> or <tcti-option-config> results in the default being used for that portion respectively. 🌈

🎯 TCTI Defaults

When a TCTI is not specified, the default TCTI is searched for using dlopen(3) semantics. The tools will search for tabrmd, device and mssim TCTIs IN THAT ORDER and USE THE FIRST ONE FOUND. You can query what TCTI will be chosen as the default by using the -v option to print the version information. The "default-tcti" key-value pair will indicate which of the aforementioned TCTIs is the default. 🔍

🛠️ Custom TCTIs

Any TCTI that implements the dynamic TCTI interface can be loaded. The tools internally use dlopen(3), and the raw tcti-name value is used for the lookup. Thus, this could be a path to the shared library, or a library name as understood by dlopen(3) semantics. bring your own TCTI, we love a DIY moment 💅

🧩 TCTI OPTIONS

This collection of options are used to configure the various known TCTI modules available:

  • device: For the device TCTI, the TPM character device file for use by the device TCTI can be specified. The default is /dev/tpm0.

Example: -T device:/dev/tpm0 or export TPM2TOOLS_TCTI="device:/dev/tpm0"

  • mssim: For the mssim TCTI, the domain name or IP address and port number used by the simulator can be specified. The default are 127.0.0.1 and 2321.

Example: -T mssim:host=localhost,port=2321 or export TPM2TOOLS_TCTI="mssim:host=localhost,port=2321"

  • abrmd: For the abrmd TCTI, the configuration string format is a series of simple key value pairs separated by a , character. Each key and value string are separated by a = character.
    • TCTI abrmd supports two keys:
      1. bus_name : The name of the tabrmd service on the bus (a string).
      2. bus_type : The type of the dbus instance (a string) limited to session and system.

Specify the tabrmd tcti name and a config string of bus_name=com.example.FooBar:

\--tcti=tabrmd:bus_name=com.example.FooBar

Specify the default (abrmd) tcti and a config string of bus_type=session:

\--tcti:bus_type=session
NOTE: abrmd and tabrmd are synonymous. the various known TCTI modules. 🫶

and that's where part one lands, bestie — more coming 💖

✨ EXAMPLES ✨

Ok bestie these are the actual recipes, and honestly? each one eats 💅

🎀 Create an RSA key and load it

Three steps, no skipping, they're a set:

tpm2_createprimary -c primary.ctx
tpm2_create -C primary.ctx -Grsa2048 -u key.pub -r key.priv
tpm2_load -C primary.ctx -u key.pub -r key.priv -c key.ctx

Primary first (that's your main character energy context), then you make the actual RSA key with -Grsa2048 and split it into a public part (-u key.pub) and a private part (-r key.priv), then you load both halves back into key.ctx. Now you've got a loaded key. Slay 💖

🔥 Encrypt using RSA

echo "my message" > msg.dat
tpm2_rsaencrypt -c key.ctx -o msg.enc msg.dat

Drop your message in a file, hand it to the TPM with the loaded context key.ctx, and out comes msg.enc. Locked, sealed, iconic 🦋

🌸 Decrypt using RSA

tpm2_rsadecrypt -c key.ctx -o msg.ptext msg.enc
cat msg.ptext
my message

Round trip!! tpm2_rsadecrypt takes msg.enc and gives you back msg.ptext, and when you cat it you get exactly:

my message

Literally the same message you started with. No cap, the vibe check passed 😭💜

💀 Returns

Tools can return any of the following codes — like, any of them, so don't come for me when you get a 2:

  • 0 — Success. We love her 🎀
  • 1 — General non-specific error.
  • 2 — Options handling error.
  • 3 — Authentication error.
  • 4 — TCTI related error.
  • 5 — Non supported scheme. Applicable to tpm2_testparams.
Fr fr if you get a 5 on this page, you're probably messing with tpm2_testparams — it's not your girl's problem 💀

🐛 BUGS

Github Issues — that's where you go, that's where the bugs live 🧚

🫶 HELP

See the Mailing List — the whole squad is there, they're nice, they'll help you 🔥

👑 License

This work is licensed under the Creative Commons Attribution 4.0 International License (CC BY 4.0).

And that's the whole page, bestie! 🌈💖 This gorgeous thing comes to you from tpm2-tools and lives at tpm2_rsaencrypt(1) — shoutout to the tpm2-tools crew and their doc build for the version and the date, mwah 🎀💅✨

📦 where this page comes from