Is error propagation in DES PCBC a good method to prevent decryption/crypt analysis by third parties?
If I had a very large file encrypted with Perl's DES with the PCBC option, and then removed the first megabyte of the resulting ciphertext would this render the remaining ciphertext 100% immune to crypt analysis ? Why or why not? Suppose that the missing 1 megabyte file disappeared forever would the ciphertext never be able to be decrypted? I'm assuming that too much information is being lost by not having the first megabyte of the ciphertext for it ever to be decrypted or any further information about the plaintext to be discovered.
What if the data was encrypted first in AES-CBC for more protection and then re-encrypted with DES PCBC for the intended error propagation? Could this weaken it or would it strengthen it slightly?
I am considering using the PERL DES cipher with the PCBC option since this seems to be the easiest and fastest way to implement this.