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

A trust assertion describes a level of trust in a certain subject for a given purpose. Conceptually each trust assertion is a triple containing the following: Reference to the Subject Purpose Level of Trust We examine each of these parts of the triple in further detail below.

XXX Untrusted: Explicitly untrusted. Override other trust. Unknown: The trust is not known and should be determined elsewhere. Trusted: Explicitly trusted. Override other trust

A trust assertion refers to a specific purpose or usage. A certificate may be trusted for purposes like: email, code signing, authenticating a server. In addition to the usage, the purpose can contain a more specific designation, such as the hostname of a server. The purpose can be a wildcard which matches any purpose. This is especially useful for untrusted assertions.

Each trust assertion contains a reference to the subject. This is the thing that is trusted. In this specification we will deal exclusively with certificates as the subject. However . There are two ways to refer to a certificate depending on whether that certificate is being referred to as a trust root (like a certificate authority) or referred to by another trusted certificate. Certificates used as trust roots are referred to by the complete DER encoding of the certificate. Certificates verified by another certificate (signed as part of a certificate chain) are referred to by the DER value of the issuer field and the serial number. Referring to a trust root certificate by its issuer and serial number is meaningless. Referring to a certificates signed by another certificate would preclude uses such as certificate revocation lists. Therefore different methods MUST be used to refer certificates in these different situations.

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_G_TRUST_ASSERTION and have the following attributes. Attribute Data Type Description CKA_CLASS CK_OBJECT_CLASS CKO_G_TRUST_ASSERTION CKA_G_TRUST_TYPE CK_TRUST_TYPE CKT_G_TRUST_ROOT CKA_G_CERTIFICATE_VALUE Byte array DER SHA1 hash of the the DER-encoding of certificate. Required for self-signed certificates. CKA_G_PURPOSE CK_UTF8_CHAR array XXX CKA_G_LEVEL CK_TRUST_LEVEL The trust level of this assertion Attribute Data Type Description CKA_CLASS CK_OBJECT_CLASS CKO_G_TRUST_ASSERTION CKA_G_TRUST_TYPE CK_TRUST_TYPE CKT_G_TRUST_EXCEPTION CKA_ISSUER Byte array DER-encoding of the certificate issuer name CKA_SERIAL_NUMBER Byte array DER-encoding of the certificate serial number CKA_G_PURPOSE CK_UTF8_CHAR array XXX CKA_G_LEVEL CK_TRUST_LEVEL The trust level of this assertion Value Description CKT_G_UNTRUSTED Explicitly untrusted. Overrides trust determined elsewhere. CKT_G_UNKNOWN Trust is unknown and should be determined elsewhere. CKT_G_TRUSTED Explicitly trusts the certificate in the assertion.

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_G_TRUST_ASSERTION CKA_G_TRUST_TYPE CKT_G_TRUST_ROOT CKA_G_CERTIFICATE_VALUE XXX CKA_G_PURPOSE XXX CKA_G_TRUST_LEVEL CKL_G_TRUSTED

A C_FindObjects operation is done using the following attributes. Attribute Value CKA_CLASS CKO_NETSCAPE_TRUST CKA_G_TRUST_TYPE CKT_G_TRUST_EXCEPTION CKA_ISSUER XXX CKA_SERIAL_NUMBER XXX CKA_G_PURPOSE XXX CKA_G_TRUST_LEVEL CKL_G_UNTRUSTED

NSS: Who?

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