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Eric Wild
e03530f89a
SCP.overhead was so far set at construction time (SCP02: 8, SCP03: s_mode), so the C-MAC length only. Unfortunately sec lvl >= 3 pads the data field to the cipher block size before encryption, so the real worst-case overhead is larger, scc.max_cmd_len (255 - overhead) was too big, and ADF_SD.load() used a hardcoded chunk_len=240. Real world issue with a 286 byte CAP + SCP02 + sec lvl 3: - 240-byte LOAD block is padded to 248, - encrypted - gets 8 byte C-MAC appended -> Lc = 256 That dies with a weird "ValueError: bytes must be in range(0, 256)". The only "fix" for that was to downgrade the seclevel. STORE DATA has the same overflow with large max_cmd_len (247 + padding + MAC = 256 as well). Therefore the overhead must be properly calculated from the sec level. While at it adjust the error in case I missed something to get a more useful ValueError. Change-Id: Ic208f3959a38896f64fb6ccefb24cc360a3ac3a2