A single cosigner signature, as it appears inside the TLS-encoded MTCProof
defined by
draft-ietf-plants-merkle-tree-certs, Section 6.1:
struct {
TrustAnchorID cosigner_id;
opaque signature<0..2^16-1>;
} MTCSignature;
opaque TrustAnchorID<1..2^8-1>;
The cosigner ID is the binary trust anchor ID per Section 3 of
draft-ietf-tls-trust-anchor-ids — the base-128 OID-component bytes
only, without the ASN.1 RELATIVE-OID tag or length octets. See
TrustAnchorIDs for converting to/from the dotted-decimal form.