doc: Add a binding document for COT descriptors
Added a binding document for COT descriptors which is going to be used in order to create COT desciptors at run-time. Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com> Change-Id: Ic54519b0e16d145cd1609274a00b137a9194e8dd
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Manish V Badarkhe
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Chain of trust bindings
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=======================
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The device tree allows to describes the chain of trust with the help of
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certificates and images nodes, which in turn contains number of sub-nodes
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(i.e. certificate and image) mentioning properties for every certificate
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and image respectively.
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Also, this binding allows to describe OID of non-volatile counters, memory
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mapped address and size of non-volatile counter register.
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Convention used in this document
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--------------------------------
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This document follows the conventions described in the Device-tree
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Specification
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certificates, certificate and extension node bindings definition
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----------------------------------------------------------------
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- Certificates node
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Description: Container of certificate nodes.
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PROPERTIES
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- compatible:
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Usage: required
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Value type: <string>
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Definition: must be "arm, certificate-descriptors"
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- Certificate node
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Description: Describes certificate properties which are used
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during the authentication process.
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PROPERTIES
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- root-certificate
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Usage: Required for the certificate with no parent.
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In other words, Certificates which are validated
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using root of trust public key.
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Value type: <boolean>
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- image-id
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Usage: Required for every certificate with unique id.
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Value type: <u32>
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- parent
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Usage: It refers to their parent image, which typically contains
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information to authenticate the certificate.
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This property is required for all non-root certificates.
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This property is not required for root-certificates
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as it is validated using root of trust public key
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provided by platform.
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Value type: <phandle>
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- signing-key
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Usage: This property is used to refer extension node present in
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parent certificate and it is required property for all non-
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root certificates which are authenticated using public-key
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present in parent certificate.
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This property is not required for root-certificates
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as root-certificates are validated using root of trust
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public key provided by platform.
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Value type: <phandle>
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- antirollback-counter
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Usage: This property is used by all certificates which are protected
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against rollback attacks using a non-volatile counter and it
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is optional property.
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This property is used to refer trusted or non-trusted
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non-volatile counter node.
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Value type: <phandle>
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SUBNODES
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- extensions node
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Description: This is sub-node of certificate node.
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Describes OIDs present in the certificate which will
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be used during authentication process to extract
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hash/public key information from this certificate.
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OIDs in extension node are represented using number of
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sub-nodes which contains 'oid' as property
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PROPERTIES
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- oid
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Usage: This property provides the Object ID of an extension
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provided in the certificate.
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Value type: <string>
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Example:
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.. code:: c
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certificates {
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compatible = "arm, certificate-descriptors”
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trusted-key-cert: trusted-key-cert {
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root-certificate;
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image-id = <TRUSTED_KEY_CERT_ID>;
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antirollback-counter = <&trusted_nv_counter>;
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extensions {
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trusted-world-pk: trusted-world-pk {
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oid = TRUSTED_WORLD_PK_OID;
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};
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non-trusted-world-pk: non-trusted-world-pk {
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oid = NON_TRUSTED_WORLD_PK_OID;
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};
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};
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};
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scp_fw_key_cert: scp_fw_key_cert {
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image-id = <SCP_FW_KEY_CERT_ID>;
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parent = <&trusted-key-cert>;
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signing-key = <&trusted_world_pk>;
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antirollback-counter = <&trusted_nv_counter>;
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extensions {
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scp_fw_content_pk: scp_fw_content_pk {
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oid = SCP_FW_CONTENT_CERT_PK_OID;
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};
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};
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};
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.
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.
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.
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next-cert {
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};
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};
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Images and image node bindings definition
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-----------------------------------------
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- Images node
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Description: Container of image nodes
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PROPERTIES
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- compatible:
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Usage: required
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Value type: <string>
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Definition: must be "arm, image-descriptors"
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- Image node
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Description: Describes image properties which will be used during
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authentication process.
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PROPERTIES
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- image-id
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Usage: Required for every image with unique id.
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Value type: <u32>
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- parent
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Usage: Required for every image to provide a reference to
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it's parent image, which contains the necessary information
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to authenticate it.
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Value type: <phandle>
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- hash
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Usage: Required for all images which are validated using
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hash method. This property is used to refer extension
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node present in parent certificate and it is required
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property for all images.
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Value type: <phandle>
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Note: Currently, all images are validated using "hash"
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method. In future, there may be multiple methods can
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be used to validate the image.
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Example:
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.. code:: c
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images {
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compatible = "arm, imgage-descriptors";
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scp_bl2_image {
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image-id = <SCP_BL2_IMAGE_ID>;
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parent = <&scp_fw_content_cert>;
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hash = <&scp_fw_hash>;
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};
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.
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.
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.
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next-img {
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};
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};
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non-volatile counter node binding definition
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--------------------------------------------
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- non-volatile counters node
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Description: Contains properties for non-volatile counters.
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PROPERTIES
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- compatible:
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Usage: required
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Value type: <string>
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Definition: must be "arm, non-volatile-counter"
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- #address-cells
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Usage: required
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Value type: <u32>
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Definition: Must be set according to address size
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of non-volatile counter register
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- #size-cells
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Usage: required
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Value type: <u32>
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Definition: must be set to 0
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SUBNODE
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- counters node
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Description: Contains various non-volatile counters present in the platform.
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PROPERTIES
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- reg
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Usage: Register base address of non-volatile counter and it is required
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property.
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Value type: <u32>
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- oid
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Usage: This property provides the Object ID of non-volatile counter
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provided in the certificate and it is required property.
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Value type: <string>
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Example:
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Below is non-volatile counters example for ARM platform
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.. code:: c
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non-volatile-counters {
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compatible = "arm, non-volatile-counter";
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#address-cells = <1>;
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#size-cells = <0>;
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counters {
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trusted-nv-counter: trusted_nv_counter {
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reg = <TFW_NVCTR_BASE>;
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oid = TRUSTED_FW_NVCOUNTER_OID;
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};
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non_trusted_nv_counter: non_trusted_nv_counter {
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reg = <NTFW_CTR_BASE>;
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oid = NON_TRUSTED_FW_NVCOUNTER_OID;
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};
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};
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};
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Future update to chain of trust binding
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---------------------------------------
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This binding document need to be revisited to generalise some terminologies
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like Object IDs, extensions etc which are currently specific to X.509
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certificates.
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*Copyright (c) 2020, Arm Limited and Contributors. All rights reserved.*
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@ -19,3 +19,4 @@ Components
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secure-partition-manager-design
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psa-ffa-manifest-binding
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xlat-tables-lib-v2-design
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cot-binding
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