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I'm trying to figure out the format/encoding for this:

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 to replicate it with my own public key.

I've looked at this https://crypto.stackexchange.com/questions/41871/how-to-find-the-encoding-of-an-rsa-public-key and from what I can see there are similarities, though it doesn't seem to be the same as that.

orangedoggo
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1 Answers1

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00040000 looks like a 32 bit value representing the length of the data.

If we decode it in little-endian we get 1024:

sage: int.from_bytes(bytes.fromhex('00040000'), 'little')
1024

I'm assuming this gives the number of bits that follow; the next 1024 bits (n) are:

f21a03ef61ad05c0af8d2acf29d3d779c2f73b61aa88533dac358410ac7a08d005dbd6325bb5064eb8afb24e3aef680cfad779d854b7ef97d4f5a1f2f16eb63ebf1b1235f89b65053c01f68a19bcda4183516c20cd907a49301d1314f956fbcc2018e4cfe6991c224d0e177eb11d7fae8477cd6701580754cc116782a0b6b6db

Followed by 1024 bits (e) that are

0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000010001

The latter is very likely the exponent, however in big-endian:

sage: int.from_bytes(bytes.fromhex('00010001'), 'big')
65537

65537 is a very commonly used exponent.

Since e is in big-endian, I assume n is too, so your public modulus is:

sage: int.from_bytes(bytes.fromhex('f21a03ef61ad05c0af8d2acf29d3d779c2f73b61aa88533dac358410ac7a08d005dbd6325bb5064eb8afb24e3aef680cfad779d854b7ef97d4f5a1f2f16eb63ebf1b1235f89b65053c01f68a19bcda4183516c20cd907a49301d1314f956fbcc2018e4cfe6991c224d0e177eb11d7fae8477cd6701580754cc116782a0b6b6db'), 'big')
170009540932613151769038469988293650218844004053584339002200232194264352712884216925985784801458591501781573072892989116728048997832334682982748978655741179946010134561466243581524386945399240608537896417387019700398948330733836779231824938918338194668413830256507020494474648180467264074322450994971415066331

Then, there is another public key of the same length 00040000 with the same e 00010001.

It's public modulus is:

sage: int.from_bytes(bytes.fromhex('af5105fa343e9d8e72294fb8e752a703f54f9b403826f8dd06cf2628ece496806e182ab0e88591f6c0ee7873cb69409e735c62105dd2e28bd45428806836cdb8d94b204ace06d342d24ed824c6988b7db3bd840b50071d291aa4a8cda9187a3f698616fb8ae398f0011a3e38ef31312f07aba316b35858d8e5fe7e7ef8c01209'), 'big')
123111431213688323191113429717081285154340099011946618199498087171573056754335780131987080307395734064403880657942875702088682210145904820435534801337217797703105810136529933603381871426734823683013576987571192787312359697878601542181638347168216122667608679225431011863788903839101406098646701462875195576841
ambiso
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