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184 lines
8.2 KiB
C
184 lines
8.2 KiB
C
/******************************************************************************
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*
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* THIS SOURCE CODE IS HEREBY PLACED INTO THE PUBLIC DOMAIN FOR THE GOOD OF ALL
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*
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* This is a simple and straightforward implementation of AES-GCM authenticated
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* encryption. The focus of this work was correctness & accuracy. It is written
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* in straight 'C' without any particular focus upon optimization or speed. It
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* should be endian (memory byte order) neutral since the few places that care
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* are handled explicitly.
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*
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* This implementation of AES-GCM was created by Steven M. Gibson of GRC.com.
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*
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* It is intended for general purpose use, but was written in support of GRC's
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* reference implementation of the SQRL (Secure Quick Reliable Login) client.
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*
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* See: http://csrc.nist.gov/publications/nistpubs/800-38D/SP-800-38D.pdf
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* http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/ \
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* gcm/gcm-revised-spec.pdf
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*
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* NO COPYRIGHT IS CLAIMED IN THIS WORK, HOWEVER, NEITHER IS ANY WARRANTY MADE
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* REGARDING ITS FITNESS FOR ANY PARTICULAR PURPOSE. USE IT AT YOUR OWN RISK.
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*
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*******************************************************************************/
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#pragma once
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#define GCM_AUTH_FAILURE 0x55555555 // authentication failure
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#include "aes.h" // gcm_context includes aes_context
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#if defined(_MSC_VER)
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#include <basetsd.h>
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typedef unsigned int size_t;// use the right type for length declarations
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typedef UINT32 uint32_t;
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typedef UINT64 uint64_t;
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#else
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#include <stdint.h>
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#endif
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/******************************************************************************
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* GCM_CONTEXT : GCM context / holds keytables, instance data, and AES ctx
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******************************************************************************/
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typedef struct {
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int mode; // cipher direction: encrypt/decrypt
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uint64_t len; // cipher data length processed so far
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uint64_t add_len; // total add data length
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uint64_t HL[16]; // precalculated lo-half HTable
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uint64_t HH[16]; // precalculated hi-half HTable
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uchar base_ectr[16]; // first counter-mode cipher output for tag
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uchar y[16]; // the current cipher-input IV|Counter value
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uchar buf[16]; // buf working value
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aes_context aes_ctx; // cipher context used
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} gcm_context;
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/******************************************************************************
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* GCM_CONTEXT : MUST be called once before ANY use of this library
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******************************************************************************/
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int gcm_initialize(void);
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/******************************************************************************
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* GCM_SETKEY : sets the GCM (and AES) keying material for use
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******************************************************************************/
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int gcm_setkey(gcm_context *ctx, // caller-provided context ptr
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const uchar *key, // pointer to cipher key
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const uint keysize // size in bytes (must be 16, 24, 32 for
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// 128, 192 or 256-bit keys respectively)
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); // returns 0 for success
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/******************************************************************************
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*
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* GCM_CRYPT_AND_TAG
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*
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* This either encrypts or decrypts the user-provided data and, either
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* way, generates an authentication tag of the requested length. It must be
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* called with a GCM context whose key has already been set with GCM_SETKEY.
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*
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* The user would typically call this explicitly to ENCRYPT a buffer of data
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* and optional associated data, and produce its an authentication tag.
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*
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* To reverse the process the user would typically call the companion
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* GCM_AUTH_DECRYPT function to decrypt data and verify a user-provided
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* authentication tag. The GCM_AUTH_DECRYPT function calls this function
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* to perform its decryption and tag generation, which it then compares.
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*
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******************************************************************************/
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int gcm_crypt_and_tag(
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gcm_context *ctx, // gcm context with key already setup
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int mode, // cipher direction: ENCRYPT (1) or DECRYPT (0)
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const uchar *iv, // pointer to the 12-byte initialization vector
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size_t iv_len, // byte length if the IV. should always be 12
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const uchar *add, // pointer to the non-ciphered additional data
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size_t add_len, // byte length of the additional AEAD data
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const uchar *input, // pointer to the cipher data source
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uchar *output, // pointer to the cipher data destination
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size_t length, // byte length of the cipher data
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uchar *tag, // pointer to the tag to be generated
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size_t tag_len); // byte length of the tag to be generated
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/******************************************************************************
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*
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* GCM_AUTH_DECRYPT
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*
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* This DECRYPTS a user-provided data buffer with optional associated data.
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* It then verifies a user-supplied authentication tag against the tag just
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* re-created during decryption to verify that the data has not been altered.
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*
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* This function calls GCM_CRYPT_AND_TAG (above) to perform the decryption
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* and authentication tag generation.
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*
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******************************************************************************/
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int gcm_auth_decrypt(
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gcm_context *ctx, // gcm context with key already setup
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const uchar *iv, // pointer to the 12-byte initialization vector
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size_t iv_len, // byte length if the IV. should always be 12
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const uchar *add, // pointer to the non-ciphered additional data
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size_t add_len, // byte length of the additional AEAD data
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const uchar *input, // pointer to the cipher data source
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uchar *output, // pointer to the cipher data destination
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size_t length, // byte length of the cipher data
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const uchar *tag, // pointer to the tag to be authenticated
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size_t tag_len); // byte length of the tag <= 16
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/******************************************************************************
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*
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* GCM_START
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*
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* Given a user-provided GCM context, this initializes it, sets the encryption
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* mode, and preprocesses the initialization vector and additional AEAD data.
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*
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******************************************************************************/
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int gcm_start(gcm_context *ctx, // pointer to user-provided GCM context
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int mode, // ENCRYPT (1) or DECRYPT (0)
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const uchar *iv, // pointer to initialization vector
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size_t iv_len, // IV length in bytes (should == 12)
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const uchar *add, // pointer to additional AEAD data (NULL if none)
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size_t add_len); // length of additional AEAD data (bytes)
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/******************************************************************************
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*
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* GCM_UPDATE
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*
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* This is called once or more to process bulk plaintext or ciphertext data.
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* We give this some number of bytes of input and it returns the same number
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* of output bytes. If called multiple times (which is fine) all but the final
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* invocation MUST be called with length mod 16 == 0. (Only the final call can
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* have a partial block length of < 128 bits.)
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*
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******************************************************************************/
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int gcm_update(gcm_context *ctx, // pointer to user-provided GCM context
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size_t length, // length, in bytes, of data to process
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const uchar *input, // pointer to source data
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uchar *output); // pointer to destination data
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/******************************************************************************
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*
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* GCM_FINISH
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*
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* This is called once after all calls to GCM_UPDATE to finalize the GCM.
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* It performs the final GHASH to produce the resulting authentication TAG.
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*
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******************************************************************************/
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int gcm_finish(gcm_context *ctx, // pointer to user-provided GCM context
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uchar *tag, // ptr to tag buffer - NULL if tag_len = 0
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size_t tag_len); // length, in bytes, of the tag-receiving buf
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/******************************************************************************
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*
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* GCM_ZERO_CTX
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*
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* The GCM context contains both the GCM context and the AES context.
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* This includes keying and key-related material which is security-
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* sensitive, so it MUST be zeroed after use. This function does that.
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*
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******************************************************************************/
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void gcm_zero_ctx(gcm_context *ctx);
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