Key lifetimes

Definition at line 236 of file crypto_types.h.

The maximum value for a key identifier chosen by the application.

Definition at line 1662 of file crypto_values.h.

The minimum value for a key identifier chosen by the application.

Definition at line 1659 of file crypto_values.h.

The maximum value for a key identifier chosen by the implementation.

Definition at line 1668 of file crypto_values.h.

The minimum value for a key identifier chosen by the implementation.

Definition at line 1665 of file crypto_values.h.

Construct a lifetime from a persistence level and a location.

Parameters

persistence	The persistence level (value of type psa_key_persistence_t).
location	The location indicator (value of type psa_key_location_t).

Returns

The constructed lifetime value.

Definition at line 1643 of file crypto_values.h.

Definition at line 1611 of file crypto_values.h.

Definition at line 1608 of file crypto_values.h.

Whether a key lifetime indicates that the key is volatile.

A volatile key is automatically destroyed by the implementation when the application instance terminates. In particular, a volatile key is automatically destroyed on a power reset of the device.

A key that is not volatile is persistent. Persistent keys are preserved until the application explicitly destroys them or until an implementation-specific device management event occurs (for example, a factory reset).

Parameters

lifetime

The lifetime value to query (value of type psa_key_lifetime_t).

Returns

1 if the key is volatile, otherwise 0.

Definition at line 1630 of file crypto_values.h.

The default lifetime for persistent keys.

A persistent key remains in storage until it is explicitly destroyed or until the corresponding storage area is wiped. This specification does not define any mechanism to wipe a storage area, but implementations may provide their own mechanism (for example to perform a factory reset, to prepare for device refurbishment, or to uninstall an application).

This lifetime value is the default storage area for the calling application. Implementations may offer other storage areas designated by other lifetime values as implementation-specific extensions. See psa_key_lifetime_t for more information.

Definition at line 1588 of file crypto_values.h.

Referenced by psa_set_key_id().

The default lifetime for volatile keys.

A volatile key only exists as long as the handle to it is not closed. The key material is guaranteed to be erased on a power reset.

A key with this lifetime is typically stored in the RAM area of the PSA Crypto subsystem. However this is an implementation choice. If an implementation stores data about the key in a non-volatile memory, it must release all the resources associated with the key and erase the key material if the calling application terminates.

Definition at line 1573 of file crypto_values.h.

Referenced by psa_set_key_id(), and psa_set_key_lifetime().

The local storage area for persistent keys.

This storage area is available on all systems that can store persistent keys without delegating the storage to a third-party cryptoprocessor.

See psa_key_location_t for more information.

Definition at line 1653 of file crypto_values.h.

Definition at line 1655 of file crypto_values.h.

The default persistence level for persistent keys.

See psa_key_persistence_t for more information.

Definition at line 1600 of file crypto_values.h.

A persistence level indicating that a key is never destroyed.

See psa_key_persistence_t for more information.

Definition at line 1606 of file crypto_values.h.

The persistence level of volatile keys.

See psa_key_persistence_t for more information.

Definition at line 1594 of file crypto_values.h.

Encoding of identifiers of persistent keys.

• Applications may freely choose key identifiers in the range PSA_KEY_ID_USER_MIN to PSA_KEY_ID_USER_MAX.
• Implementations may define additional key identifiers in the range PSA_KEY_ID_VENDOR_MIN to PSA_KEY_ID_VENDOR_MAX.
• 0 is reserved as an invalid key identifier.
• Key identifiers outside these ranges are reserved for future use.

Definition at line 235 of file crypto_types.h.

Encoding of key lifetimes.

The lifetime of a key indicates where it is stored and what system actions may create and destroy it.

Lifetime values have the following structure:

• Bits 0-7 (PSA_KEY_LIFETIME_GET_PERSISTENCE(lifetime)): persistence level. This value indicates what device management actions can cause it to be destroyed. In particular, it indicates whether the key is volatile or persistent. See psa_key_persistence_t for more information.
• Bits 8-31 (PSA_KEY_LIFETIME_GET_LOCATION(lifetime)): location indicator. This value indicates where the key is stored and where operations on the key are performed. See psa_key_location_t for more information.

Volatile keys are automatically destroyed when the application instance terminates or on a power reset of the device. Persistent keys are preserved until the application explicitly destroys them or until an implementation-specific device management event occurs (for example, a factory reset).

Persistent keys have a key identifier of type psa_key_id_t. This identifier remains valid throughout the lifetime of the key, even if the application instance that created the key terminates. The application can call psa_open_key() to open a persistent key that it created previously.

This specification defines two basic lifetime values:

• Keys with the lifetime PSA_KEY_LIFETIME_VOLATILE are volatile. All implementations should support this lifetime.
• Keys with the lifetime PSA_KEY_LIFETIME_PERSISTENT are persistent. All implementations that have access to persistent storage with appropriate security guarantees should support this lifetime.

Definition at line 139 of file crypto_types.h.

Encoding of key location indicators.

If an implementation of this API can make calls to external cryptoprocessors such as secure elements, the location of a key indicates which secure element performs the operations on the key. If an implementation offers multiple physical locations for persistent storage, the location indicator reflects at which physical location the key is stored.

This specification defines the following values of location indicators:

• 0: primary local storage. All implementations should support this value. The primary local storage is typically the same storage area that contains the key metadata.
• 1: primary secure element. Implementations should support this value if there is a secure element attached to the operating environment. As a guideline, secure elements may provide higher resistance against side channel and physical attacks than the primary local storage, but may have restrictions on supported key types, sizes, policies and operations and may have different performance characteristics.
• 2-0x7fffff: other locations defined by a PSA specification. The PSA Cryptography API does not currently assign any meaning to these locations, but future versions of this specification or other PSA specifications may do so.
• 0x800000-0xffffff: vendor-defined locations. No PSA specification will assign a meaning to locations in this range.

Note

Key location indicators are 24-bit values. Key management interfaces operate on lifetimes (type psa_key_lifetime_t) which encode the location as the upper 24 bits of a 32-bit value.

Definition at line 218 of file crypto_types.h.

Encoding of key persistence levels.

What distinguishes different persistence levels is what device management events may cause keys to be destroyed. Volatile keys are destroyed by a power reset. Persistent keys may be destroyed by events such as a transfer of ownership or a factory reset. What management events actually affect persistent keys at different levels is outside the scope of the PSA Cryptography specification.

This specification defines the following values of persistence levels:

• 0 = PSA_KEY_PERSISTENCE_VOLATILE: volatile key. A volatile key is automatically destroyed by the implementation when the application instance terminates. In particular, a volatile key is automatically destroyed on a power reset of the device.
• 1 = PSA_KEY_PERSISTENCE_DEFAULT: persistent key with a default lifetime. Implementations should support this value if they support persistent keys at all. Applications should use this value if they have no specific needs that are only met by implementation-specific features.
• 2-127: persistent key with a PSA-specified lifetime. The PSA Cryptography specification does not define the meaning of these values, but other PSA specifications may do so.
• 128-254: persistent key with a vendor-specified lifetime. No PSA specification will define the meaning of these values, so implementations may choose the meaning freely. As a guideline, higher persistence levels should cause a key to survive more management events than lower levels.
• 255 = PSA_KEY_PERSISTENCE_READ_ONLY: read-only or write-once key. A key with this persistence level cannot be destroyed. Implementations that support such keys may either allow their creation through the PSA Cryptography API, preferably only to applications with the appropriate privilege, or only expose keys created through implementation-specific means such as a factory ROM engraving process. Note that keys that are read-only due to policy restrictions rather than due to physical limitations should not have this persistence levels.

Note

Key persistence levels are 8-bit values. Key management interfaces operate on lifetimes (type psa_key_lifetime_t) which encode the persistence as the lower 8 bits of a 32-bit value.

Definition at line 184 of file crypto_types.h.