2.2.1.7.2 KeyInfo Element
The <KeyInfo> element is specified in [XMLDSig/2008] section 4.4 (excluding subsections). A <KeyInfo> element MUST contain exactly one <SecurityTokenReference> element as a child element, as specified in [BSP] section 8.8. The <SecurityTokenReference> element MUST conform to the definition specified in section 2.2.1.1.