Linkable Spontaneous Anonymous Group Signature for Ad Hoc Groups

An implementation of the linkable anonymous group signature scheme by Joseph K. Liu, Victor K. Wei and Duncan S. Wong described in http://eprint.iacr.org/2004/027.pdf.

The primitives used go as follows:

• $G$ is the NIST P-224 elliptic curve
• $H_1$ and $H_2$ are implemented using Keccak[]. $H(x)$ is the $H(x||i)$ with the least byte $i$ for which the result represents some element of the required group
• Private keys and other scalars are encoded as 28-byte big-endian integers
• Public keys and other elliptic curve points are encoded as a byte in {0x02,0x03} representing the sign of the $y$ coordinate followed by the $x$ coordinate.

Dependencies

• openssl
• keccak (included)

Building

gcc -c -O3 keccak/KeccakF-1600-opt32.c -o keccak/KeccakF-1600-opt32.o
gcc -c -O3 keccak/KeccakSponge.c -o keccak/KeccakSponge.o
gcc -c -O3 lsags.c -o lsags.o
gcc -O3 -o lsags-test lsags-test.c lsags.o keccak/KeccakSponge.o keccak/KeccakF-1600-opt32.o -lcrypto

Performance

Signing or verifying a message in a group with 1000 members takes about 2 seconds on Intel Core 2 Duo L9400 @ 1.86GHz.

License

GPLv3 with the exception that allows linking to OpenSSL. If you are a non-GPL open source project and would like to use the code, contact me about it.