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aes: xts: Enforce NIST SP 800-38E data unit size

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NIST SP 800-38E requites the data unit size be limited to at most 2^20 AES
blocks in size. Enforce this restriction.
This commit is contained in:
Jaeden Amero 2018-05-30 15:36:06 +01:00
parent 5162b932a2
commit 0a8b02087a
2 changed files with 12 additions and 2 deletions
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11
include/mbedtls/aes.h
View File

@ -292,10 +292,16 @@ int mbedtls_aes_crypt_cbc( mbedtls_aes_context *ctx,
* defined by a data unit number. The data unit number must be * defined by a data unit number. The data unit number must be
* provided by \p iv. * provided by \p iv.
* *
* NIST SP 800-38E limits the maximum size of a data unit to 2^20
* AES blocks. If the data unit is larger than this, this function
* returns #MBEDTLS_ERR_AES_INVALID_INPUT_LENGTH.
*
* \param ctx The AES XTS context to use for AES XTS operations. * \param ctx The AES XTS context to use for AES XTS operations.
* \param mode The AES operation: #MBEDTLS_AES_ENCRYPT or * \param mode The AES operation: #MBEDTLS_AES_ENCRYPT or
* #MBEDTLS_AES_DECRYPT. * #MBEDTLS_AES_DECRYPT.
* \param length The length of a data unit in bytes. * \param length The length of a data unit in bytes. This can be any
* length between 16 bytes and 2^24 bytes inclusive
* (between 1 and 2^20 block cipher blocks).
* \param iv The address of the data unit encoded as an array of 16 * \param iv The address of the data unit encoded as an array of 16
* bytes in little-endian format. For disk encryption, this * bytes in little-endian format. For disk encryption, this
* is typically the index of the block device sector that * is typically the index of the block device sector that
@ -309,7 +315,8 @@ int mbedtls_aes_crypt_cbc( mbedtls_aes_context *ctx,
* *
* \return \c 0 on success. * \return \c 0 on success.
* \return #MBEDTLS_ERR_AES_INVALID_INPUT_LENGTH if \p length is * \return #MBEDTLS_ERR_AES_INVALID_INPUT_LENGTH if \p length is
* smaller than an AES block in size (16 bytes). * smaller than an AES block in size (16 bytes) or if \p
* length is larger than 2^20 blocks (16 MiB).
*/ */
int mbedtls_aes_crypt_xts( mbedtls_aes_xts_context *ctx, int mbedtls_aes_crypt_xts( mbedtls_aes_xts_context *ctx,
int mode, int mode,

3
library/aes.c
View File

@ -1158,6 +1158,9 @@ int mbedtls_aes_crypt_xts( mbedtls_aes_xts_context *ctx,
if( length < 16 ) if( length < 16 )
return( MBEDTLS_ERR_AES_INVALID_INPUT_LENGTH ); return( MBEDTLS_ERR_AES_INVALID_INPUT_LENGTH );
/* NIST SP 80-38E disallows data units larger than 2**20 blocks. */
if( length > ( 1 << 20 ) * 16 )
return MBEDTLS_ERR_AES_INVALID_INPUT_LENGTH;
mbedtls_aes_crypt_ecb( &ctx->tweak, MBEDTLS_AES_ENCRYPT, iv, t_buf.u8 ); mbedtls_aes_crypt_ecb( &ctx->tweak, MBEDTLS_AES_ENCRYPT, iv, t_buf.u8 );