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Makefile: allow specifying a SHA-1 for non-cryptographic uses

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Introduce _UNSAFE variants of the OPENSSL_SHA1, BLK_SHA1, and
APPLE_COMMON_CRYPTO_SHA1 compile-time knobs which indicate which SHA-1
implementation is to be used for non-cryptographic uses.

There are a couple of small implementation notes worth mentioning:

  - There is no way to select the collision detecting SHA-1 as the
    "fast" fallback, since the fast fallback is only for
    non-cryptographic uses, and is meant to be faster than our
    collision-detecting implementation.

  - There are no similar knobs for SHA-256, since no collision attacks
    are presently known and thus no collision-detecting implementations
    actually exist.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Taylor Blau
2024-09-26 11:22:50 -04:00
committed by Junio C Hamano
parent 253ed9ecff
commit 06c92dafb8
2 changed files with 55 additions and 0 deletions
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Makefile
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@@ -521,6 +521,10 @@ include shared.mak
# Define APPLE_COMMON_CRYPTO_SHA1 to use Apple's CommonCrypto for
# SHA-1.
#
# Define the same Makefile knobs as above, but suffixed with _UNSAFE to
# use the corresponding implementations for unsafe SHA-1 hashing for
# non-cryptographic purposes.
#
# If don't enable any of the *_SHA1 settings in this section, Git will
# default to its built-in sha1collisiondetection library, which is a
# collision-detecting sha1 This is slower, but may detect attempted
@@ -1987,6 +1991,27 @@ endif
endif
endif
ifdef OPENSSL_SHA1_UNSAFE
ifndef OPENSSL_SHA1
EXTLIBS += $(LIB_4_CRYPTO)
BASIC_CFLAGS += -DSHA1_OPENSSL_UNSAFE
endif
else
ifdef BLK_SHA1_UNSAFE
ifndef BLK_SHA1
LIB_OBJS += block-sha1/sha1.o
BASIC_CFLAGS += -DSHA1_BLK_UNSAFE
endif
else
ifdef APPLE_COMMON_CRYPTO_SHA1_UNSAFE
ifndef APPLE_COMMON_CRYPTO_SHA1
COMPAT_CFLAGS += -DCOMMON_DIGEST_FOR_OPENSSL
BASIC_CFLAGS += -DSHA1_APPLE_UNSAFE
endif
endif
endif
endif
ifdef OPENSSL_SHA256
EXTLIBS += $(LIB_4_CRYPTO)
BASIC_CFLAGS += -DSHA256_OPENSSL