A data processing system (DPS) supports exchange of digital keys. The DPS comprises a communication module which, when executed by the DPS, is operable to receive, via multiple different network routes, multiple copies of a seed message from a second DPS, as part of a Diffie-Hellman key exchange process with the second DPS, wherein each copy of the seed message includes a seed value. The DPS also comprises a security module which, when executed by the DPS, is operable to perform operations comprising (a) determining a prevalent seed value, based on the multiple copies of the seed message; (b) computing a prevalence metric to indicate how many of the seed messages contained the prevalent seed value; and (c) determining whether a seed exchange portion of the Diffie-Hellman key exchange process has been successfully performed, based on the prevalence metric. Other embodiments are described and claimed.