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General Internet Engineering Task Force security pkcs11 trust x509 certificate pki PKCS#11 is a standard that defines ways to store certificates, keys and perform crypto operations. It does not specify a way to store trust assertions. Trust assertions are used to assign an explicit level of trust to a certificate. Examples of trust assertions are certificate authority root certificates, certificate revocation lists, and certificate trust exceptions. This document outlines a way to store trust assertions with PKCS#11. This is not a new design, but documentation of the method already in use by libraries such as NSS.

PKCS#11 is a useful and widely supported standard for storage and use of keys and certificates. It is often used with smart cards.

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A trust assertion describes a level of trust in an object for a given usage or purpose. Conceptually each trust assertion is a triple containing: Certificate Reference Usage or Purpose Level of Trust We examine each of these parts of the triple in further detail below.

A trust assertion ultimately denotes a level of trust. These are: Untrusted: The certificate is explicitly untrusted. Unknown: The trust is not known and should be determined elsewhere. Trusted: The certificate itself is explicitly trusted. Trusted Delegator: The certificate is trusted as a certificate authority trust root. Trust is confers to certificates that this certificate has signed, or signed certificates have signed, and so on.

A trust assertion always refers to a specific purpose or usage. A certificate may be trusted for purposes like: email, code signing, authenticating a server.

Each trust assertion contains a reference to a certificate. There are two ways to refer to a certificate depending on whether that certificate is self-signed (like a certificate authority) or signed by another trusted certificate. Self-signed certificates are referred to by their complete hash of the DER value of the certificate. Certificates signed by another certificate are referred to by the DER value of the issuer field, and the serial number. Referring to a self-signed certificate by its issuer and serial number is meaningless. Referring to a signed certificate by its hash, would preclude uses such as certificate relocation lists, which do not contain certificates or enough information to generate a hash. Therefore different methods MUST be used to refer to self-signed and issuer-signed certificates.

Trust assertions are stored as objects on a PKCS#11 token. Although these are specific to a certificate, they do not need to be stored on the same token as the certificate. Trust assertions objects are of the class CKO_NETSCAPE_TRUST and have the following attributes. Trust object attributes. Attribute Type Description CKA_CLASS CK_OBJECT_CLASS CKO_NETSCAPE_TRUST CKA_ISSUER Byte array DER-encoding of the certificate issuer name CKA_SUBJECT Byte array DER-encoding of the certificate subject name. Optional, default empty CKA_SERIAL_NUMBER Byte array DER-encoding of the certificate serial number CKA_CERT_SHA1_HASH Byte array SHA1 hash of the the DER-encoding of certificate. Required for self-signed certificates. CKA_CERT_MD5_HASH Byte array MD5 hash of the the DER-encoding of certificate. Required for self-signed certificates. CKA_TRUST_SERVER_AUTH CK_TRUST Level of trust for server authentication extended usage. CKA_TRUST_CLIENT_AUTH CK_TRUST Level of trust for client authentication extended usage. CKA_TRUST_CODE_SIGNING CK_TRUST Level of trust for code signing extended usage. CKA_TRUST_EMAIL_PROTECTION CK_TRUST Level of trust for email protection extended usage. CKA_TRUST_IPSEC_END_SYSTEM CK_TRUST Level of trust for IPSEC end system extended usage. CKA_TRUST_IPSEC_TUNNEL CK_TRUST Level of trust for IPSEC tunnel extended usage. CKA_TRUST_IPSEC_USER CK_TRUST Level of trust for IPSEC user extended usage. CKA_TRUST_TIME_STAMPING CK_TRUST Level of trust for IPSEC time stamping extended usage. CKA_TRUST_DIGITAL_SIGNATURE CK_TRUST Level of trust for digital signature key usage. CKA_TRUST_NON_REPUDIATION CK_TRUST Level of trust for non-repudiation key usage. CKA_TRUST_KEY_ENCIPHERMENT CK_TRUST Level of trust for key-encipherment key usage. CKA_TRUST_DATA_ENCIPHERMENT CK_TRUST Level of trust for data-encipherment key usage. CKA_TRUST_KEY_AGREEMENT CK_TRUST Level of trust for key-agreement key usage. CKA_TRUST_KEY_CERT_SIGN CK_TRUST Level of trust for certificate signing key usage. CKA_TRUST_KEY_CRL_SIGN CK_TRUST Level of trust for crl signing key usage. Xxxx: Possible additional attributes: CKA_TRUST_TYPE (CKT_CERTIFICATE_SELF_SIGNED, CKT_CERTIFICATE_SIGNED), CKA_CERT_SHA256_HASH CK_TRUST represenst a level of trust. Value Description CKT_UNTRUSTED Explicitly untrusted. CKT_UNKNOWN Trust is unknown and should be determined elsewhere. CKT_TRUSTED Explicitly trusts the certificate in the assertion. CKT_TRUSTED_DELEGATOR Trusts the certificate as a certificate authority.

Trust assertions are checked using a PKCS#11 C_FindObjects operation. Because trust is involved and presence/lack of results is important, this operation MUST be done with a specific set of lookup attributes. The attributes used differ depending on whether the certificate is self-signed or is signed by an issuer. Checking of trust assertions is always done for a specific purpose.

A C_FindObjects operation is done using the following attributes. Attribute Value CKA_CLASS CKO_NETSCAPE_TRUST CKA_CERT_SHA1_HASH 20 byte value of hash of certificate. Purpose attribute CKT_TRUSTED_DELEGATOR

A C_FindObjects operation is done using the following attributes. Attribute Value CKA_CLASS CKO_NETSCAPE_TRUST CKA_CERT_SHA1_HASH 20 byte value of hash of certificate. Purpose attribute CKT_TRUSTED

A C_FindObjects operation is done using the following attributes. Attribute Value CKA_CLASS CKO_NETSCAPE_TRUST CKA_ISSUER DER encoding of certificate issuer. CKA_SERIAL_NUMBER DER encoding of certificate serial number. Purpose attribute CKT_UNTRUSTED

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NSS: Who?

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Xxxx: Use of multiple PKCS#11 modules Not using just any module.

Mad Dominators, Inc.

This becomes an Appendix.