csu3_am335x/EVSE/GPL/tpm2-tools-5.1/man/common/alg.md

Algorithm Specifiers

Options that take algorithms support "nice-names".

There are two major algorithm specification string classes, simple and complex. Only certain algorithms will be accepted by the TPM, based on usage and conditions.

Simple specifiers

These are strings with no additional specification data. When creating objects, non-specified portions of an object are assumed to defaults. You can find the list of known "Simple Specifiers Below".

Asymmetric

• rsa
• ecc

Symmetric

• aes
• camellia

Hashing Algorithms

• sha1
• sha256
• sha384
• sha512
• sm3_256
• sha3_256
• sha3_384
• sha3_512

Keyed Hash

• hmac
• xor

Signing Schemes

• rsassa
• rsapss
• ecdsa
• ecdaa
• ecschnorr

Asymmetric Encryption Schemes

• oaep
• rsaes
• ecdh

Modes

• ctr
• ofb
• cbc
• cfb
• ecb

Misc

• null

Complex Specifiers

Objects, when specified for creation by the TPM, have numerous algorithms to populate in the public data. Things like type, scheme and asymmetric details, key size, etc. Below is the general format for specifying this data: <type>:<scheme>:<symmetric-details>

Type Specifiers

This portion of the complex algorithm specifier is required. The remaining scheme and symmetric details will default based on the type specified and the type of the object being created.

• aes - Default AES: aes128
• aes128<mode> - 128 bit AES with optional mode (ctr|ofb|cbc|cfb|ecb). If mode is not specified, defaults to null.
• aes192<mode> - Same as aes128<mode>, except for a 192 bit key size.
• aes256<mode> - Same as aes128<mode>, except for a 256 bit key size.
• ecc - Elliptical Curve, defaults to ecc256.
• ecc192 - 192 bit ECC
• ecc224 - 224 bit ECC
• ecc256 - 256 bit ECC
• ecc384 - 384 bit ECC
• ecc521 - 521 bit ECC
• rsa - Default RSA: rsa2048
• rsa1024 - RSA with 1024 bit keysize.
• rsa2048 - RSA with 2048 bit keysize.
• rsa4096 - RSA with 4096 bit keysize.

Scheme Specifiers

Next, is an optional field, it can be skipped.

Schemes are usually Signing Schemes or Asymmetric Encryption Schemes. Most signing schemes take a hash algorithm directly following the signing scheme. If the hash algorithm is missing, it defaults to sha256. Some take no arguments, and some take multiple arguments.

Hash Optional Scheme Specifiers

These scheme specifiers are followed by a dash and a valid hash algorithm, For example: oaep-sha256.

• oaep
• ecdh
• rsassa
• rsapss
• ecdsa
• ecschnorr

Multiple Option Scheme Specifiers

This scheme specifier is followed by a count (max size UINT16) then followed by a dash(-) and a valid hash algorithm.

• ecdaa For example, ecdaa4-sha256. If no count is specified, it defaults to 4.

No Option Scheme Specifiers

This scheme specifier takes NO arguments.

• rsaes

Symmetric Details Specifiers

This field is optional, and defaults based on the type of object being created and it's attributes. Generally, any valid Symmetric specifier from the Type Specifiers list should work. If not specified, an asymmetric objects symmetric details defaults to aes128cfb.

Examples

Create an rsa2048 key with an rsaes asymmetric encryption scheme

tpm2_create -C parent.ctx -G rsa2048:rsaes -u key.pub -r key.priv

Create an ecc256 key with an ecdaa signing scheme with a count of 4 and sha384 hash

/tpm2_create -C parent.ctx -G ecc256:ecdaa4-sha384 -u key.pub -r key.priv