How is 4G LTE encrypted? Is 4G secure?

The answer to - Is 4G secure is that Information regarding the current implementation of "4G" LTE, as well as the soon to be deployed true 4G LTE-A, can be found at the European Telecommunications Standards Institute (ETSI) website and portal.

3G networks use the KASUMI block cipher with the UEA1 confidentiality and UIA1 integrity algorithms. As you said, there have been several demonstrated weaknesses, which has prompted the use of a new cipher / algorithm. The 4G LTE successor is the SNOW 3G stream cipher and the UEA2 confidentiality and UIA2 integrity algorithms. To quote the specs page: SNOW 3G is a word-oriented stream cipher that generates a sequence of 32-bit words under the control of a 128-bit key and a 128-bit initialisation variable. These words can be used to mask the plaintext. First a key initialisation is performed, i.e. the cipher is clocked without producing output, see 4.1. Then with every clock tick it produces a 32-bit word of output.