halacha - What is the source that forbids indecent dress by women?

I have been hardpressed finding a source for something that would seem to be such a well known Halacha. I (and most other too probably) have been brought up with the belief that it is forbidden for a girl to walk around indecently. What that exactly is depends on whom you ask, with many opinions saying a skirt must reach 4 inches below the knee.

Where does anyone even mention such an Issur in the Torah before 100 years ago?

Here are some Pshatim I have heard.

1. 
   

   Most people tend to quote the Issur of praying in front of an Ervah, however this is an Issur on Dvorim Shebikdusha and does not dictate how a lady must dress?

   
   


2. 
   

   People bandy about with the term לִפְנֵ֣י עִוֵּ֔ר לֹ֥א תִתֵּ֖ן מִכְשֹׁ֑ל (Lifnei Iver Loh Siten Michshol). However this should then subject it to the many rules of Lifnei Iver, upon which many leniencies should then apply. For example, one could say there are other ways a man has access to Hirhur and Histaklus, even if those would actually cost him money (Rema 151:1)

   
   



3. 
   

   Another Pshat I heard is that like the Gemoro deduces a woman must cover her hair from the fact it says Uporah Rosh HaIsha, so too we can deduct that she must cover her body because it says you shall uncover her top. This seems to me like a nice Vort, but I dont think we can make Droshos for ourselves.

   
   

Is it simply common sense but it was too obvious to be recorded in Halacha? If so, where do the Shiurim of x amount of inches come from? Was it common sense to use the Ervah guidelines used for Dvarim Shebikdusha?