I'll use 1. AES-256-CBC 2. RSA with > 8192 key 3. Triple DES 4 Blowfish 5. Twofish 6. CHACHA20
I'm still not sure in which order to use them but please list disadvantages of using this method except size of cypher text.
Honestly, just stick to one algorithm and use that. Choose something modern. There is no evidence that AES-256 has problems. CBC mode allows some alteration of the plaintext but it's limited and noticeable, best to include an integrity check (HMAC or CMAC).
You really don't want to encrypt bulk data using RSA, it's simply not designed for that.
It's a story of a clever kid, relying on intuitions and getting it wrong, because it's mathematics.
Thus he devotes one of his twelve chapters entirely to random numbers.
Unfortunately, it is well established by internet forums that nobody should read Knuth.
What if AES-256 gets compromised?
Basically i'm storing my encrypted data online. Anyone can see it but only i can decrypt it.
A symmetric cipher is a permutation, multiple symmetric ciphers in sequence is still a permutation. There has been no analysis done on the latter to determine if the sequence you use hides a weakness. I'd much prefer a well analysed system to an unanalysed one.
No its not. The data feeding to the next algorithm is an already encrypted data from the previous algorithm. Theres 0 connection b/w them.
For example . step 1 . encrypt message (M) with key (K1) using AES to produce cipher text (C1) step 2 . encrypt message C1 with key K2 using TripleDES to produce C2. step n . and so on using all algorithms with different Keys.
I don't see any connections b/w them. 0 entropy. Please correct me if i'm wrong.
The bottom line is just AES is good enough. Your data almost certainly isn't worth the effort involved for an attacker even if there was a substantial breakthrough against AES. If it was worth enough, there are far cheaper and easier ways to get access than breaking the crypto: https://xkcd.com/538/
Modern symmetric crypto is secure enough: any problems you hear about are not in the algorithms. Cracking crypto as seen in movies is a complete fiction, it doesn't work like that.
I suggest reading some introductory texts on cryptography to fill knowledge gaps.
There's no disadvantage in terms of algorithmic secrecy.
While I can't offer you a formal cryptanalysis, I do have a handwave-y thought experiment & proof by contradiction for intuition:
Consider two encryption algorithms A[...] and B[...] that are "good" in the standard ways (adversary cannot decrypt messages without keys, keys cannot be leaked by chosen plaintext attack, etc).
If putting A inside of B like B[A[...]] renders the system insecure, it would imply that B[...] was not a "good" encryption function! (if it was good, it would not break just because the input message happens to be the output of A[...]).
Therefore by handwave-y proof by contradiction, if A[...] and B[...] are "good", then A[B[...]] should be OK.
(Disclaimer: Again, this is a casual thought experiment and not real cryptanalysis. This result may not be true under formal cryptanalysis.)