The block checksum is used at POLYAS to prevent votes from being manipulated after submission to the ballot box. For this purpose, a block is formed after every 30 votes received. The votes are arranged at random, making it impossible to trace which vote was received at what time. The block is used to calculate a SHA-256 checksum. The checksum is written to the electoral roll after each block. From the second block onwards, the previous checksum is included. If a vote is manipulated, the checksum of the block and all subsequent checksums no longer match those of the ballot box. POLYAS CORE 3.0 offers methods for the direct verification of the online voting process. Verifiability in POLYAS CORE 3.0 is facilitated by cryptography methods: Zero-knowledge proofs provide transparency of the mixing process, decryption and counting of the ballot papers, while maintaining voting secrecy.