India for many years since 1947 was only focused on its backyard, so the intelligence gathering only was limited to Pakistan, the other neighbors and China. It is only in the last 5 years that other countries have entered the ambit of India in a major way where it becomes imperative to know and gather intelligence about them. To develop assets takes a lot of time and effort. Unfortunately the low level mantris that have been in charge of defence and so on have little knowledge or inclination for the nuances of this. In a fit of stupidity they have thrown away assets developed over several years. One does not have to look far. There was an a***hole PM called Inder Gujral in India. The family still exists as wheeler dealers in Delhi, one brother was an architect. India had over the years developed assets to report on the Pakistani nuclear weapons program. In a fit of "aman ka tamasha" and bonhomie and "friendliness" Gujral revealed to the Pakistanis all the names of Indian intelligence operatives who were reporting the status of the Pakistani nuclear program. They were rounded up and executed and a veil of silence descended on that program. Such is the flippancy intelligence was treated by the highest in the land.
Indian intelligence was restricted to having a cipher clerk in Pakistan in the pay, a person who could take a photoshot of a document in a diplomatic bag in Sri Lanka etc etc It is now that a need has arisen to go beyon the small fry and it will take time. Do not forget during WW2, Japan was an "inscrutable Asian" with a complete veil. It is to the credit of the Americans that they had a marvellous codebreaking team before the war started. Sinkov, Friedman and Rochefort are the great codebreakers. They managed to break PURPLE the top Japanese diplomatic code and then the Japanese Imperial navy codes which enabled them to break the back of the Japanese at Midway and kill Admiral Isakoru Yamamoto while he was on an inspection flight to Rabaul. These are great achievements of Mathematics that ripped the fight out of Japan. At no time during the war were there human assets inside the Japanese systems. Contrast this today with the immense internet traffic, satellites and massive computers. So a lot of collation of data etc can be done by computers and AI.
Whether code breaking institutions exists in India is a guess. Whether it is at the level of Fort Meade off I 95 between Baltimore and Washington DC, who knows. Fort Meade recruits top Number Theory PhD students from US universities for its many programs.
For sure there are no courses on related Mathematics in ANY Indian syllabus or an IIT, just coolie level stuff by gas balls. Friedman also was instrumental having a Ghaddar Party guy arrested and imprisoned who was sending messages using a book code, Hermaba Lal Gupta. The book by David Kahn which I read 45 years ago and has been since updated is a thrilling account of Codebreaking
https://www.amazon.com/Codebreakers-Com ... 0684831309
One things is also certain, the Israelis also have a top program and recruit top notch products from Tel Aviv University ad the Technion Israel Institute of Technology in Haifa.
Books on the mathematical aspects of Codebreaking are beyond members of this forum, frankly you lack the prerequisites.