Your contact must have given you their key's fingerprint, made up of 40 hexadecimal characters.
The key owner must have allowed their key to be searched by email. The search covers the full email entered, as contained in the public key.
To verify an ARISTHOR signature, use our public key, which you can find by entering this fingerprint [ b540b9742249d5465e0c437e7f604e617b3e8c5d ] (without the brackets) in the search field above, or by getting it directly here Aristhor's public key