The Huawei S7721U, like most carrier-grade equipment, employs a Secure Boot or Verified Boot mechanism. During the Power-On Self-Test (POST), the bootloader reads the recovery image (typically a compressed filesystem containing the kernel, initramfs, and recovery utilities) and computes a cryptographic hash or verifies a digital signature against an embedded public key. This signature is calculated over the image's header, kernel, ramdisk, and device tree. Any alteration—even a single byte changed in a configuration file, a replaced driver module, or an attempt to downgrade to an older firmware—will cause the hash mismatch. The error message is the bootloader’s final verdict: "Trust is broken. Halt."
Resources and tools (brief list)
Navigate to the extracted folder. Look for a file named recovery.img or a SquashFS filesystem with offset 0x200000 . huawei s7721u recovery image verify failed repack
A very specific and technical topic!