Rump Session, CHES 2004August 12, 2004 How to Securely Implement Cryptosystems Against Side-Channel Attacks on General Purpose Cryptographic Hardware Filipe Rosado da-Fonseca Portugal

Rump Session, CHES 2004August 12, 2004 Common Implementation 1.The cryptosystem to implement is selected. 2.The cryptosystem is implemented by use of the functions made available by the cryptographic hardware's APIs.

Rump Session, CHES 2004August 12, 2004 Cryptographic Hardware's APIs 1.Non-cryptographic Functions (xor, and, or, not,...): protected against simple side-channel attacks. 2.Cryptographic Primitives (RSA, AES, SHA-1,...): protected against both simple and differential side-channel attacks.

Rump Session, CHES 2004August 12, 2004 Example: CBC-MAC T K (M) { if ((|M|=0)  ((|M| mod 128)≠0)) then return error; n_m:=|M|/128; for(j:=1; j≤n_m; j++) m j :=M[(j-1)*128...j*128-1]; y 0 := > 128 ; for(i:=1; i≤n_m; i++) { x1 i :=xor(m i, y i-1 ); y i :=AES K (x1 i ); } tag:=y n_m ; return tag; }

Rump Session, CHES 2004August 12, 2004 Secure Implementation 1.The cryptosystem to implement is selected. 2.The cryptosystem is tested for leakages. If leakages are found, then one goes back to step 1. Otherwise, one goes to step 3. 3.The cryptosystem is implemented by use of the functions made available by the cryptographic hardware's APIs.

Rump Session, CHES 2004August 12, 2004 Questions and Further Information Annotated Slides: SCA1 Model: