CryptoExportImportManager | swift class for exporting and importing public keys | SSH Utils library

I am attempting to hash and sign user data on iOS (14.4), send that to my server, and have the server verify the hash and the signature with a previously uploaded public key (sent on keypair generation during user creation). It seems a number of people have run into issues with this, but all of the answers I've been able to find are very old, don't factor in using Apple's Secure Enclave, or revolve around signing and verifying on the same iOS device.

The general workflow is: User creates an account on iOS, and a random keypair is created on the device with the private key remaining in the Secure Enclave, while the public key is converted to ASN.1 format, PEM encoded and uploaded to the server. When the user later signs data, the data is JSONEncoded, hashed with sha512, and signed by their private key in the Secure Enclave. This is then packaged into a base64EncodedString payload, and sent to the server for verification. The server first verifies the hash using openssl_digest and then checks the signature using openssl_verify.

I have been unable to get the openssl_verify method to successfully verify the signature. I have also attempted using the phpseclib library (to get more insight into why the verification fails) without success. I understand phpseclib uses the openssl library if it is available, but even if this is disabled, phpseclib's internal verification fails because the resulting values after modulus do not match. Interestingly, phpseclib converts the public key to what looks like PKCS8 formatting with a large amount of padding.

It appears the public key is being parsed and loaded properly by openssl, as a proper reference is being created prior to verification. However, since the private key is opaque (residing in the Secure Enclave) I don't have a way to externally "check" how the signatures themselves are generated/encoded or if the same signature would be created outside of the iOS device. I'm wondering if I have an encoding error, or if external verification is possible with keys generated in the Secure Enclave.

iOS Public Key Upload method- I am using CryptoExportImportManager which converts the raw bytes to DER, adds the ASN.1 header, and adds the BEGIN and END key tags.