8051 and AVR Cryptolibrary
Skein hash and ThreeFish block cipher NEW!
Skein is a proposed hash function, submitted to the SHA-3 competition. Based around a new block cipher called ThreeFish. Both will certainly receive attention and cryptoanalysis in the forthcoming SHA-3 process.
Although these are certainly more heavy-weight than needed for most of applications in this class of microcontrollers, it might be interesting to study them as a counterpoint of the much more lightweight ciphers presented on these pages. See the table at bottom of page for performance figures. A few more words on these implementations here.
Both implementations are for Skein-256-256 and ThreeFish 256 with 256-bit (32-byte) block and key size.
- Skein-256-256 and ThreeFish-256 for 8052 - hash and encryption
- Skein-256-256 and ThreeFish-256 for AVR - hash and encryption
TEA
Data block and key length are 64 bits.- TEA for '51 - encryption/decryption
- XTEA for '51 - encryption/decryption
- TEA for AVR - encryption
- XTEA for AVR - encryption/decryption
XTEA for SDCC
The XTEA cipher only slightly modified as an SDCC function, together with an appropriate header and an example test "application".
Both encryption and decryption is implemented; if only one of these is needed, comment the corresponding #define in xtea.h. The original implementation in C provided for reference.
Usage:
- include xtea.h into your application
- define a secret key as an "initialized" array of 16 bytes (or 4 longints, or any similar scheme) in code memory
- fill in 8 bytes of plaintext (ciphertext, if decription is to be used rather than encryption) into the global xtea_data.b array (alternatively, into the xtea_data.l.x and xtea_data.l.y long int variables)
- call xtea(&key) (xtea_i(&key) for decryption)
- ciphertext (plaintext in case of decryption) is now in the xtea_data.b array
- it is enough to have only encryption selected using the #defines in xtea.h
- define a secret key as above
- before first usage, fill in the xtea_data.b array with "random" seed (e.g. based on timer, keyboard input, or similar "random" input), or store/restore the current value of seed in nonvolatile memory
- to generate one pseudorandom number, call xtea(&key)
- use (part of) the ciphertext as the pseudorandom number (observe proper "handling" (e.g. scaling) of pseudorandom numbers)
- re-seed xtea_data.b xoring with "real randomness" regularly.
SkipJack
Data block and key length are 64 bits.- SkipJack for '51 - encryption/decryption
- SkipJack for '51 (fast version) - encryption/decryption
- SkipJack for '51 (fast register-based version) - encryption/decryption
- SkipJack for AVR (fast version) - encryption/decryption
SEA
All implementations are for 96-bit data block and 96-bit key, based on 8-bit word size.- SEA for '51 - encryption(Sea)+decryption(iSea)+both ways(EDSea)
- SEA for AVR - encryption(Sea)+decryption(iSea)+both ways(EDSea), including a version with compromise between speed and size (Sea2 - encryption only)
'51
tea.a51 xtea.a51 skipjack.a51 skipfast.a51 skipregs.a51 sea.a51-Sea sea.a51-EDSea ThreeFish-256
size(bytes) 206 218 364 1428 1140 524 604 2543
cycles 9350 6952 1682 788 788 7878 8250 12760
kB/sec 2.9 3.8 15.9 33.8 33.8 5.1 4.8 8.4
tea_i.a51 xtea_i.a51 skipj_i.a51 skipf_i.a51 skipr_i.a51 sea.a51-iSea
size(bytes) 213 224 364 1444 1156 524
cycles 9436 7051 1683 804 804 7878
kB/sec 2.8 3.8 15.9 33.2 33.2 5.1
AVR
tea.asm xtea.asm skipfast.asm sea.asm-Sea sea.asm-EDSea sea.asm-Sea2 ThreeFish-256
size(bytes) 2*94=188 2*103=206 2*942=1884 2*417=834 2*453=906 2*225=450 2*2446=4892
cycles 6861 6347 901 9658 9937 10906 10564
kB/sec 18.7 20.2 142.1 19.9 19.3 17.6 48.5
Please note, that SEA uses 96-bit key, while TEA and SkipJack use only 64-bit key. ThreeFish-256 uses a 256-bit key.
Remark: kB/sec values are based on 20MHz 6-clock '51(RD2) and 16MHz AVR.