Is there any practical difference from using
HMAC-SHA1(key, msg) vs
SHA1(key + msg) as a way to verify the authenticity/integrity of a certain message? Note that the plus sign means string concatenation in this context
Am I losing out on some esoteric detail that the
HMAC-SHA1 offers in terms of mathematical immunity to cryptanalysis? Or do both approaches basically do the same thing?
Ive looked through the basic descriptions of both algorithms. And although
HMAC-SHA1 seems to do some fancy things with padding and other stuff, I fail to understand any importance. To me both
HMAC-SHA1(key, msg) &
SHA1(key + msg) carry essentially the same strength/resistance against attacks aside from superficial details
How am I wrong, What am I missing?