Coco-Ibex

Repo which contains the design of the secured Ibex core, as shown in COCO: Co-Design and Co-Verification of Masked Software Implementations onCPUs.

The design is based on commit #863fb56eb166d of the original Ibex core.

Structure

• rtl: contains the hardware design of the modified Ibex core.
  • secure.sv: allows to enable/disable certain security features
• shared/rtl: contains the secure RAM implementation

Enabling/disabling security features

We implemented the following security features:

• REGREAD_SECURE: gating mechanism for reads from the register file
• REGWRITE_SECURE: gating mechanism for writes to the register file
• MEM_SECURE: use secure RAM
• MD_SECURE: gating mechanism for multiplication unit
• SHIFT_SECURE: gating mechanism for shifter in ALU
• ADDER_SECURE: gating mechanism for adder in ALU
• CSR_SECURE: gating mechanism for CSR unit

Each of these features is standalone, i.e., disabling REGREAD_SECURE but enabling all other features will still work. Disabling can be done by uncommenting the respective line in secure.sv.

We did not add an enabling/disabling mechanism for clearing the hidden LSU state.

Configuring secure RAM

Configurations can be made by altering a and b in ram_1p_secure.v:

• a: number of 32-bit cells per block
• b: number of blocks

In-block addressing is done using one-hot encoded addresses.