I am writing a contract in solidity for verifying multiple signature schemes.I found that solidity supports ECDSA, but how do I add check for RSA and Ed25519. is there any existing method/library developed that can be used?
RSA signature verification is possible in ethereum by virtue of EIP-198. You can see an example usage in modExp function in this answer. There is a draft EIP-665 for Ed25519 signature verification. This is not final yet.