Determining a cryptographic algorithm by description I found a signing algorithm while analyzing obfuscated source code.

I only have a basic knowledge about cryptography.  I want any clue that can help me to figure out if is a known and named cryptographic algorithm or a variant, if is strong and breakable, or how the signer generates the signature.

The point is if this is a case of an unbreakable algorithm stop and not try anything, or continue my work trying to break.

The Algorithm:

Having $\mathit{message}$ and $\mathit{signature}$ clearly separated in a file:



First calculate a $\mathit{message\_digest}$:



$\mathit{message\_digest} = \mathrm{padding} \mathop\Vert \operatorname{SHA-1}(\mathit{message})$

Where
$\mathrm{padding} = 0001 \mathop\Vert \mathrm{ff}(105\ \mathrm{times}) \mathop\Vert 00 = $
0001FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF00



And then check if this expression is true:



$\mathit{signature}^3 \equiv \mathit{message\_digest} \pmod{\mathit{key}}$

Where $\mathit{key} =$ 
C01D9FD2747B89681255F0C934610183CB45E2C57E511DBB4D651D2AD1F9B4E91D31169D3D444F91074A8EAF3F688EEC9E0E5E76F52CAF61A6ECC4A5A2154997755754E68D7C6BC1EE9C2B64B03C3157E83242A8AA8311371354363FAE8D0D5C843CEB0844FB2C3C499E1C41313A729000550038363AEF2BF8E20346B36C6B65



I have also found the follow signed message in the source code that I analise:

For a message that i know  with $\mathit{message\_digest} = $
1FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF008CBB319AB06BA3F4E05625984ED2D89E42C51813

The $\mathit{signature}\ =$
5D3C1672CC314D8E50D302790D3BE9FB0CC5286A0D050BD83EA920B0F90C8E86A95E471CD34C3F81DDA89A14DE03781266F623975BD8B9CB95608EAFDE8426A7E0AEFA60DD80E76A652397D466674E439EADB30103F9A15F4EE6022DFCB8D36CBFABE1D922BBE5C7011242AE5DBAB7A35BF7C970BB1B45563176A5CFE3CBC23A
It's RSA signature validation, using the PKCS-1.5 signature padding, with $e=3$, and the RSA modulus given by $\mathit{key}$.

It's a circa 1024 bit key; assuming $\mathit{key}$ is a properly chosen RSA modulus, nowadays it would be considered potentially breakable (in the sense that you could recover the private key, and hence be able to sign any message you want), however it would be a major effort.

If you're asking whether you can trust it, well, probably not; a well funded adversary could likely break it.  If you're asking whether you can break it, well, no; you're not a well funded adversary.