I did not have a restriction code, then the resource com.apple.restrictionspassword.plist :
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict/>
</plist>
I tried change the restriction passcode to 1234, and now: (in bold)
........
<dict>
<key>RestrictionsPasswordKey</key>
<data>
S6PcLATheGi4xsdSmsVplFDFhjI=
</data>
<key>RestrictionsPasswordSalt</key>
<data>
6rqQuw==
</data>
</dict>
.....
I remove the restriction key, and I set the key 1234 again:
......
<dict>
<key>RestrictionsPasswordKey</key>
<data>
W53yNhyVx4lOF8ibsGDxpI0VOfk=
</data>
<key>RestrictionsPasswordSalt</key>
<data>
Ag/X9g==
</data>
</dict>
.......
The value of <RestrictionsPasswordKey> and <RestrictionsPasswordSalt> are different, but the key is the same 1234.
If I fail by entering the code, I get : 1 failed attempt
I can see this on the resource com.apple.springboard.plist
<key>SBParentalControlsFailedAttempts</key>
<integer>1</integer>
iPhone 5, iOS 7.0.4