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Supposedly, if an R or S value will equal a "negative" number, one must append zeros to it and alter the "length" descriptor for the value to reflect that. When manually creating a raw tx how does one determine whether one's R and or S values require the addition of these extra byte(s)? All conversions I do with a hex calculator always show positive numbers.
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If the first byte is greater than or equal to 0x80 (128), then you need to add a leading zero byte. You can do 0x80 & first_byte. If the result is zero, no padding is needed.
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There are unsigned and signed numbers. R + S values are obviously interpreted as signed numbers, and when the first bit of the number is high, then you have a number, which is interpreted as negative. So all signatures' S and R values beginning with "more than 7F"
Pieter explained it here: extract:
