ECC Key Formatting

The format for public and private keys depends on the command and key length. In general, the Most Significant Bytes (MSB) appear first on the bus and at the lowest address in memory. In the remainder of this section below, the bytes on the left side of the page are the MSBs. Microchip recommends all pad bytes be set to zero for consistency.

When a public key is configured to be validated by the Verify command, the Most Significant four bits of the first byte in memory are used internally by the device to save the validation state. They are always set to the invalid state (0xA) by the Write command, and then may be set to the Valid state (0x5) by the Verify command.

The lowest levels of the I/O protocols are described below. Above the I/O protocol level, the exact same bytes are transferred to and from the device to implement the commands. Error codes are documented in the following sections.