why don't people read what was said in other comments before replying 
the ONLY problem here is the encoding of the signature that when it generates r and s, r is 32 bytes, s is 31 bytes. it doesn't pad s so it ends up with a 64 (1+32+31) byte signature instead of 65 (1+32+(1+31)).
if you change that, the signature becomes valid. try the following and see for yourself:
this is NOT a problem with Electrum, at least not the new versions. i DID test it with my own key and brute forced a signature with a smaller r or s and it DID generate the right signature encoding.
your signature length is invalid, it should have been 65 bytes but what you posted here is only 64 bytes which means it is missing 1 byte.
this should not have happened, i can't see any bugs that could lead to this either. are you sure that you have not modified the signature yourself?
the ONLY problem here is the encoding of the signature that when it generates r and s, r is 32 bytes, s is 31 bytes. it doesn't pad s so it ends up with a 64 (1+32+31) byte signature instead of 65 (1+32+(1+31)).
if you change that, the signature becomes valid. try the following and see for yourself:
Code:
IFkS40AxIuRGDN/vnjwavfV6R00h3MKArtDB7tpBbnqIADHOlkhiEJv8JuJTeyVW2Oo23jH9u8fFTqiOms4MM9k=
this is NOT a problem with Electrum, at least not the new versions. i DID test it with my own key and brute forced a signature with a smaller r or s and it DID generate the right signature encoding.
3. the signature I get: IFkS40AxIuRGDN/vnjwavfV6R00h3MKArtDB7tpBbnqIMc6WSGIQm/wm4lN7JVbY6jbeMf27x8VOqI6azgwz2Q==
your signature length is invalid, it should have been 65 bytes but what you posted here is only 64 bytes which means it is missing 1 byte.
this should not have happened, i can't see any bugs that could lead to this either. are you sure that you have not modified the signature yourself?
Right, in fact I have said the same
.. might be some strange combination of characters that mislead Electrum's signer.
but you are more specific and precise.
