I guess that still many PKIs are based on RSA which hampers the migration to ECC. Nonetheless, the SSH clients in some Linux distriubtions already prefer the use of ECDSA rather than RSA or DSA.

an algorithm RSA.. it easy in manual process and in programming it;s not too difficult to implemented

I think ECC is complicated and tricky to implement securely, particularly the standard curves.

Dear Salem,

Please see the following link about the Next-generation elliptic-curve cryptography :

https://cr.yp.to/talks/2016.02.18/slides-djb-20160218-4x3.pdf

Many Thanks Dr. Rezaeipour 

ECC is more better than RSA in terms of Key length. But the main issues are implementation. I think RSA is more easy to implement than ECC

Adding to the answer of Ruhul Amin

For Encryption and some related tasks ECC expands the message two times. Furthermore, some of the points (x,y) are missing in almost every ECC curve

yes , ECC is better. You can check the below links to implement it or XOR 'ing in different ways on the basis of your needs.

Regards

Mahi

http://fm4dd.com/openssl/eckeycreate.htm

http://www.lasca.ic.unicamp.br/media/publications/amc-final.pdf

https://rosettacode.org/wiki/Elliptic_curve_arithmetic

Using frobenius endomorphism can elliminate elliptic doubling in scalar multiplication on Koblitz Curve

RSA is more used than ECC because it is older than ECC is the people who use RSA have paid a lot of money to use RSA, so it's a money problem

The main reasons might be the ones already said by Günther and Abdelhakim: RSA is just much older than ECC and thus more often used.

But I think that this is developing in the direction of ECC getting more and more used. Especially in embedded devices and for IoT stuff, ECC has just many big advantages over RSA. The key sizes and thus the encryption speed of ECC outperforms RSA significantly.

Regarding the answers that RSA is easier to implement: This might be the case for textbook RSA, which is of course super easy to implement. But for a real-life implementation, textbook RSA is also super insecure and there has to be a lot more work done for a secure implementation. Also, there are now a lot of cryptographic software libraries that should be used for bigger software programs (when developing not for embedded systems) and that provides good implementations of ECC (NaCl and libsodium are two that come to my mind).

Regarding the message expansion: I do not really get the point here. Even if a ECC 256 bit encryption expandes the message twice, we only get 512 bit, which is much smaller than RSA's 2048 bit. And that some (x, y) points are missing on a curve is also not problematic in my opinion.