Is Masah on
long boots that cover the ankles permissible if not why?

What are the conditions for something to be classified as a Khuf or Jowrab? 

Answer: 

If the boot is of such a nature that it does not prevent the toes from bending and facing in the direction of Qibla in Sajda, then Masah on in it will be permissible (provided that the other necessary conditions of Masah on the socks are met), otherwise not. In other words the front of the boot should not be so hard that it prevents the toes from bending.

[Re:- Fataawa Faridiyya Pg. 103 Vol.2].

Socks made of leather are referred to as Khuffain whilst Jowrabain refer to socks that are free of leather but manufactured from a thick type of material, wherein all the qualities and requisites of Khuffain are found.

[Re:- Thamaratun Najah Pg. 165 Vol. 1]

For a leather sock to be classified as Khuffain the following requirements should be met;

1. The sock must cover the ankles.

2. One must be able to walk wearing the socks (for a distance of 3 miles without tearing).

3. The sock must be free from being torn to the extent that the amount of three baby toes are exposed. If the sock is torn less than the above amount, then Masah on it will be valid.

4. It must hold onto the feet without being tied (onto the ankles),

5. Water should not be able to seep through and reach the skin.

6. The front portion of the feet equivalent to the measurement of three 3 baby fingers should be present. If the front portion of the feet (to this extent) is not found and only the rear part of the feet is found then Masah on leather socks will not be valid. [Re:- Nurul Idha Chapter of Masah on Khuffain]

7. The socks should not be transparent of semi transparent.

As for Jowrabain; The material of the sock should be so thick and coarse that one is able to walk with it for a distance of three miles without it tearing; it must hold onto the shin by itself without falling; water shouldn’t penetrate through the socks and neither should the socks be transparent or semi transparent. [Re:- Fataawa Faridiyya Pg. 98 Vol. 2]