Bit Allocation of Payload Metadata
| MT51 Payload Metadata | ||
|---|---|---|
| Section | Bits | Value |
| Germane Service Provider ID | 5 | WAAS, EGNOS, MSBAS, GAGAN, et al. |
| Germane Key Level | 2 | 0 - Spare |
| 1 - ECDSA AES key to decrypt Level 1 ECDSA Public Key | ||
| 2 - ECDSA Level 2 Public Key | ||
| 3 - TESLA Hash Path End Hash Point | ||
| Germane Key Hash | 16 | Truncated Unsalted 16-bit Hash of Entire Germane Key |
| Germane Key Expiration | 32 | Absolute GPS time (i.e., seconds since GPS epoch) of Germane Key Expiration |
| Authenticating Key Hash | 16 | Truncated Unsalted 16-bit Hash of Entire Authenticating Key |
| Payload Type | 2 | 0 - Public Key, AES Decryption Key, or Hash Path End |
| 1 - Authenticating pseudorandom data derived from the Authenticating Key | ||
| 2 - Spare | ||
| 3 - Core Constellation Broadcast Ephemerides Authentication | ||
| Payload Segment Number | 4 | The ordered segment number of Germane authenticating pseudorandom data |
| Parity Bit | 1 | Parity bit for a compressed public key |
| Spare | 6 | Additional features possible discussed in Section 4.1 |
| Sum Total | 84 | |
Note: To distinguish the key updated with a specific MT51 and the key used to authenticate that MT51, we call the key associated with the MT51-delivered payload the Germane Key and the key used to authenticate that delivered key the Authenticating Key.