In this usage, the term means difficult to guess. An encryption algorithm is intended to be unbreakable (in which case it is as strong as it can ever be), but might be breakable (in which case it is as weak as it can ever be) so there is not, in principle, a continuum of strength as the idiom would seem to imply: Algorithm A is stronger than Algorithm B which is stronger than Algorithm C, and so on.
Smart Clothing is made from fabrics that are wireless and washable that integrate computing fibers and materials into the integrity of the fabrics. Georgia Tech is one university among several, which include MIT and University of California at Davis, that conduct research in the area of intelligent fabric.
The term retro fashion (also known as vintage inspired) refers to new clothing, shoes, and accessories that are designed to resemble clothing, shoes, and accessories that are at least 13 years old or older. Vintage fashion (or vintage clothing) refers to the original (old) clothing the new designs are based on. So in simple terms, new clothes that look old are called retro and clothes that look old because they are old are called vintage.