From 30243ad73957a2e1cc4aedc3f23be66cdf399f00 Mon Sep 17 00:00:00 2001 From: Michael Brown Date: Fri, 28 Oct 2022 16:27:10 +0100 Subject: [crypto] Add concept of cipher alignment size The GCM cipher mode of operation (in common with other counter-based modes of operation) has a notion of blocksize that does not neatly fall into our current abstraction: it does operate in 16-byte blocks but allows for an arbitrary overall data length (i.e. the final block may be incomplete). Model this by adding a concept of alignment size. Each call to encrypt() or decrypt() must begin at a multiple of the alignment size from the start of the data stream. This allows us to model GCM by using a block size of 1 byte and an alignment size of 16 bytes. As a side benefit, this same concept allows us to neatly model the fact that raw AES can encrypt only a single 16-byte block, by specifying an alignment size of zero on this cipher. Signed-off-by: Michael Brown --- src/include/ipxe/crypto.h | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) (limited to 'src/include/ipxe/crypto.h') diff --git a/src/include/ipxe/crypto.h b/src/include/ipxe/crypto.h index 842f2f633..ba09c9468 100644 --- a/src/include/ipxe/crypto.h +++ b/src/include/ipxe/crypto.h @@ -51,8 +51,24 @@ struct cipher_algorithm { const char *name; /** Context size */ size_t ctxsize; - /** Block size */ + /** Block size + * + * Every call to encrypt() or decrypt() must be for a multiple + * of this size. + */ size_t blocksize; + /** Alignment size + * + * Every call to encrypt() or decrypt() must begin at a + * multiple of this offset from the start of the stream. + * (Equivalently: all but the last call to encrypt() or + * decrypt() must be for a multiple of this size.) + * + * For ciphers supporting additional data, the main data + * stream and additional data stream are both considered to + * begin at offset zero. + */ + size_t alignsize; /** Authentication tag size */ size_t authsize; /** Set key -- cgit v1.2.3-55-g7522