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document overhead

This commit is contained in:
Michele Balistreri 2017-09-25 10:53:04 +03:00
parent a69bd8a0df
commit 0276f29198
1 changed files with 4 additions and 0 deletions
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SECURE_CHANNEL.MD
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@ -61,6 +61,10 @@ To decrypt the data both the card and the client do the following:
2. The remaining data is decrypted using AES in CBC mode using the session key.
3. The padding is removed.
Because AES in CBC mode requires the data field length in bytes to be a multiple of 16, the maximum effective APDU
size becomes 240 bytes. Of these 16 bytes are used for the IV and minimum of 1 byte for padding, making the maximum
payload size in a single APDU 223 bytes, meaning about a 13,5% overhead.
### Error conditions
1. If a sensitive command is received without an active Secure Channel, the card shall respond with SW 0x6985 (