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SDLS Protocol Padding concept

SDLS Protocol Padding concept. Ignacio Aguilar Sanchez (ESA) CCSDS Spring Meeting 2010 | Portsmouth, VA. Padding description.

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SDLS Protocol Padding concept

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  1. SDLS ProtocolPadding concept Ignacio Aguilar Sanchez (ESA) CCSDS Spring Meeting 2010 | Portsmouth, VA

  2. Padding description • External Padding is required for some encryption and authentication algorithms that operate with input data blocks of 128-bit whenever input data length is not a block multiple. • Encryption example: Cipher Block Chaining (CBC); • Authentication example: CBC-MAC; • 1 flag in security header (padding signalling flag) to signal presence or absence of padding • limit padding to cases where it is needed; • CCSDS recommended cryptographic algorithms do not require external padding. • Padding signalling flag is authenticated • as part of security header, which is always authenticated. • If padding is present security header includes 1 octet, placed at the end of the security header, to indicate the number of padding bits (0-127) • Padding pattern does not need to be transmitted; • Padding convention: 1, 10, 100, 1000, 10000,…known as ISO/IEC 9797-1 Padding Method 2. • Padding is granular at bit level.

  3. Open points (1) • Padding signalling flag management alternatives: • Per frame • SDLS protocol determines need of padding and length for every frame and sets signalling flag accordingly; • Security header length can vary between frames; variation to be considered and accommodated by SDLS to determine SDLS output data length. • Per mission (preferred) • SDLS indicates presence of padding for all frames; • Padding length can include ‘0’ value (i.e., no padding); • Security header length is equal for all frames; simpler SDLS prediction of output data length.

  4. Open points (2) • Security: • Suitability of proposed padding pattern has been studied for CBC and CBC-MAC; assessment required for other algorithms. • Definition of padding pattern and corresponding security can be left to implementer if algorithms other than above are used; recall that CCSDS recommended algorithms do not require padding; text to be added in BB and GB accordingly.

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