object-alg.md 4.7 KB
Supported Public Object Algorithms
Supported public object algorithms are:
Symmetric
AES
The AES cipher has a bitsize and a mode. When the mode is not specified, ie a "NULL" mode, the TPM will allow any mode usages on subsequent key uses. If the mode is specified during object creation, only that mode is allowed in subsequent use cases.
aes - Default AES selection. The default AES Selection is AES 128 with a NULL mode.
aes[128|192|256] - AES with a key size of 128, 192 and 256 respectively with a NULL mode.
aes[128|192|256][cbc|ocb|cfb|ecb] - AES with a key size of 128, 192 and 256 and a mode of cbc, ocb, cfb and ecb respectively.
Examples
aes256cbc - AES with a key bitsize of 256 and a mode of cbc.
aes192cfb - AES with a bitsize of 192 and mode of cfb.
aes128 - AES with a bitsize of 128 and NULL mode.
Asymmetric
RSA
The RSA cipher has a bitsize, and the TPM (optionally) supports associating a symmetric key along with the RSA algorithm. The AES key will be used for encryption modes that rely on an RSA scheme, like RSAES_OAEP.
rsa - Default RSA algorithm. The default bitsize is 2048. Depending on if the object is a restricted object (aka a parent object), the algorithms encryption options will default to:
restricted object - scheme of null and a NULL symmetric algorithm.
non-restricted object - scheme of null and an aes128cfb symmetric algorithm.
rsa[1024|2048|4096] - Similar to rsa option, but provides control over the key size to either 1024, 2048 or 4096 respectively.
rsa[1024|2048|4096]:[oaep|rsaes] - Similar to rsa[1024|2048|4096] option, but provides the ability to control the scheme. The algorithms encryption options will default to: aes128cfb.
rsa[1024|2048|4096]:[oaep|rsaes]:[aes] Similar to rsa[1024|2048]:[oaep|rsaes] option, but provides full control over the aes key options. See the section AES for details of these AES strings.
Examples
rsa1024 - Creates an RSA 1024 key with a scheme and symmetric algorithm dependent on the restricted attribute.
rsa:oeap:aes - Creates an RSA 2048 key with an AES-OEAP scheme and an AES default key based on attributes.
rsa1024:null:aes128cbc - Creates an RSA 1024 key with a NULL encryption scheme and an AES key of 128 for use ONLY with CBC.
ECC
The ECC cipher has a size, and the TPM (optionally) supports associating a symmetric key along with the ECC algorithm. The AES key will be used for encryption modes that rely on an asymmetric encryption scheme, like RSAES_OAEP.
ecc - Default ECC algorithm. The default curve size is 256. Depending on if the object is a restricted object (aka a parent object), the algorithms encryption options will default to:
restricted object - scheme of null and a NULL symmetric algorithm.
non-restricted object - scheme of null and an aes128cfb symmetric algorithm.
ecc[224|256|384|521] - Similar to ecc option, but provides control over the curve size to either 224,256,384 or 521 respectively.
ecc[224|256|384|521]:[oaep|rsaes] - Similar to ecc[224|256|384|521] option, but provides the ability to control the scheme. The algorithms encryption options will default to: aes128cfb.
ecc[224|256|384|521]:[oaep|rsaes]:[aes] Similar to ecc[224|256|384|521]:[oaep|rsaes] option, but provides full control over the aes key options. See the section AES for details of these AES strings.
Examples
ecc224 - Creates an ECC 224 key with a scheme and symmetric algorithm dependent on the restricted attribute.
ecc:oeap:aes - Creates an ECC 256 key with an AES-OEAP scheme and an AES default key based on attributes.
ecc384:null:aes128cbc - Creates an ECC 384 key with a NULL encryption scheme and an AES key of 128 for use ONLY with CBC.
KeyedHash
The keyedhash algorithms are hmac and xor.
HMAC
The HMAC algorithm needs a hashing algorithm and nothing more. It defaults to sha256 if not specified.
- hmac:[sha256|sha384|sha512] - Generate an HMAC key valid for the associated hash algorithm, defaults to sha256 if not specified.
XOR
The XOR algorithm needs a hashing algorithm and nothing more. It defaults to sha256 if not specified. The XOR scheme should be used where confidentiality of the objects is desired, but secrecy is not mandatory. The algorithm is lightweight and quick.
- xor:[sha256|sha384|sha512] - Generate an XOR key valid for the associated hash algorithm, defaults to sha256 if not specified.
NOTE: Your TPM may not support all algorithms.