I am using ED25519 from core/java.
When an ECP point P = (x,y) is encoded into bytes (toBytes(byte[] b, boolean compress)) with compress set to true, it does not always decompress into an ECP with the same y value, i.e., it gives P' = (x, y'). A sample of ECP compression/decompression I have:
Original P:
(40ccd876746fb401023a49469c0b7f52725ec08e2b6e3ed15af0a90f445dc129,6e313f6097112eefbeeefc4ab187e32f0a00a963332a695540be983cd4798e92)
Compressed and decompressed P:
(40ccd876746fb401023a49469c0b7f52725ec08e2b6e3ed15af0a90f445dc129,ee313f6097112eefbeeefc4ab187e32f0a00a963332a695540be983cd4798e7f)
where only the first byte and the last byte of y and y' are different.
However, I noticed the point multiplication for both gives the same R = rP = rP'.
My workaround is to call mul(new BIG(1)) so the decompressed ECP always returns the same P.
May I know if is this the supposed way to perform point compression/decompression?
Clarification is appreciated, thanks!
I am using ED25519 from core/java.
When an ECP point P = (x,y) is encoded into bytes (
toBytes(byte[] b, boolean compress)) with compress set to true, it does not always decompress into an ECP with the same y value, i.e., it gives P' = (x, y'). A sample of ECP compression/decompression I have:where only the first byte and the last byte of y and y' are different.
However, I noticed the point multiplication for both gives the same R = rP = rP'.
My workaround is to call
mul(new BIG(1))so the decompressed ECP always returns the same P.May I know if is this the supposed way to perform point compression/decompression?
Clarification is appreciated, thanks!