How to find a congruence to the type of that simple equation without factoring the modulus?

[Laël Cellier <lael.cellier@laposte.net>]

> > Bonjour,simple question. I ve B and a semiprime A which are very large
> > unrelated fixed integers impossible to factor.How to find y and z such as
> > y²≡z²×B mod A? Which pari functions to use? Nfroots? Cordialement,

> You best bet is zncoppersmith, but this will only work if there is a solution
(y,z) with relatively small y and z which will almost never be the case.

> You need fundamentaly new ideas.

> Cheers,
> Bill.

Hi, sorry for the delay.
And if I’m free to chose B² mod A (thereby being indirectly free to chose B), and thus only A can’t be chosen, would it be something easy to make y and z findable through zncoppersmith as a result, and if yes, how ?
Sincerely,