The Centre told the SC on Thursday that an important reason for keeping the price of Rafale jets a secret was to prevent other countries, which have also bought the jets, from questioning France why the planes were sold cheaper to India. Documents attached with the review petition compromised national security and could be inimical to friendly ties with foreign countries, the govt said.

from Times of India https://timesofindia.indiatimes.com/india/revealing-rafales-cheap-price-will-violate-deal-govt/articleshow/68417649.cms