Digital Signature with DSA

[KWSW]

Got a question:

I managed to generate a key pair with DSA and have no problems signing and verifying with them.

But I need to attach the signature to the start of a file and have the receiver receive the file, check the signature before processing the rest of the file.

Is there a fixed length for the key size so that the receiver knows how many of the bytes in the start of the file is for the signature?

Thanks

[dav3]

I by no means have any knowledge of this subject, or how long your sign. would be. But if its stored at the beginning of the file, could the recipient not just read the first line of the file to get the sign.?

This of course would only work if the length of the sign. was < than the size of a line.

[KWSW]

I did a bit of a test and found out the lengths varies abit from 46 to 48 even though i was signing the same thing.

Decided to write the length of the signature to at the start of the file but am still trying to find out if there is a better way...