A quantum computer can find hash collisions in the square root of the time a classical computer can using Grover's algorithm. (So a 256-bit hash becomes as difficult as a 128-bit hash to reverse). Symmetric encryption (e.g. AES) is the same, so encryption itself doesn't have any problems with quantum computing (if you consider 128-bit AES to be safe in general).

Quantum computing affects the distribution of symmetric keys using public key encryption (and so affects a large amount of encryption as used in people's daily lives) which is vulnerable to quantum computers with sufficient bits.