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TPM_20_E_MODE
A symmetric algorithm, its key size and its mode form one TPM parameter set. Selecting a recognized cipher does not make every mode valid. In particular, a mode that is acceptable for an ordinary symmetric object is not automatically valid when the same field is used as the companion symmetric definition of an asymmetric parent.
Parent-key rule that matters
For an ordinary non-derivation parent, the TPM structure rules require a supported block cipher and CFB mode in the parent parameter area. The TPM can reject a template even when the host cryptography library supports the requested mode.
- Inspect the full
TPMT_SYM_DEF_OBJECT: algorithm, key bits and mode. - Determine whether the object is a restricted decryption key or a regular symmetric object.
- Do not assume that a NULL mode has the same meaning in every structure; its validity depends on the type that references it.
TCG: symmetric definitions and parent-object rules · tpm2-tools: AES sizes and modes · tpm2_create: object template options
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