Jamming-resistant communication is crucial for safety-critical applications such as emergency alert broadcasts or the dissemination of navigation signals in adversarial settings. In such applications, mission-critical messages are broadcast to a large and unknown number of (potentially untrusted) receivers that rely on the availability, integrity, and authenticity of the messages; here, availability primarily refers to the ability to communicate in the presence of jamming. Common techniques to counter jamming-based denial-of-service attacks such as Frequency Hopping (FH) and Direct Sequence Spread Spectrum (DSSS) cannot be applied in such settings because they depend on secret pairwise or group keys shared between the sender and the receivers before the communication. This dependency entails serious or unsolvable scalability and keysetup problems or weak jamming-resistance (a single malicious receiver can compromise the whole system). As a solution, in this work, we propose uncoordinat...