From 9246d041500b96fb0694cbda1d833e420696827e Mon Sep 17 00:00:00 2001
From: Chris Jones <christopher.jones@arm.com>
Date: Wed, 25 Nov 2020 15:12:39 +0000
Subject: [PATCH 01/11] Fix potential DoS by limiting number sizes in
 exponentiation

Check that the exponent and modulus is below `MBEDTLS_MPI_MAX_BITS` before
performing a time expensive operation (modular exponentiation). This prevents
a potential DoS from Diffie-Hellman computations with extremely
large key sizes.

Signed-off-by: Chris Jones <christopher.jones@arm.com>
---
 library/bignum.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/library/bignum.c b/library/bignum.c
index 9325632b4..9a70ccdf1 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -2115,6 +2115,10 @@ int mbedtls_mpi_exp_mod( mbedtls_mpi *X, const mbedtls_mpi *A,
     if( mbedtls_mpi_cmp_int( E, 0 ) < 0 )
         return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
 
+    if( mbedtls_mpi_bitlen( E ) > MBEDTLS_MPI_MAX_BITS ||
+        mbedtls_mpi_bitlen( N ) > MBEDTLS_MPI_MAX_BITS )
+        return ( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
+
     /*
      * Init temps and window size
      */

From 0c5875fd0c42d9a8ceda6f290cada6d641da1bae Mon Sep 17 00:00:00 2001
From: Chris Jones <christopher.jones@arm.com>
Date: Thu, 26 Nov 2020 11:21:53 +0000
Subject: [PATCH 02/11] Test that overly large Diffie-Hellman keys are rejected

Add a test case to ensure `mbedtls_mpi_exp_mod` fails when using a key size
larger than MBEDTLS_MPI_MAX_SIZE.
Add a test case to ensure that Diffie-Hellman operations fail when using a key
size larger than MBEDTLS_MPI_MAX_SIZE.

Signed-off-by: Chris Jones <christopher.jones@arm.com>
---
 tests/suites/test_suite_dhm.data | 3 +++
 tests/suites/test_suite_mpi.data | 5 ++++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/tests/suites/test_suite_dhm.data b/tests/suites/test_suite_dhm.data
index 4e884f465..351ec840a 100644
--- a/tests/suites/test_suite_dhm.data
+++ b/tests/suites/test_suite_dhm.data
@@ -22,6 +22,9 @@ dhm_do_dhm:10:"3":10:"5":MBEDTLS_ERR_DHM_MAKE_PARAMS_FAILED
 Diffie-Hellman zero modulus
 dhm_do_dhm:10:"0":10:"5":MBEDTLS_ERR_DHM_BAD_INPUT_DATA
 
+Diffie-Hellman huge modulus
+dhm_do_dhm:16:"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":10:"5":MBEDTLS_ERR_DHM_MAKE_PARAMS_FAILED+MBEDTLS_ERR_MPI_BAD_INPUT_DATA
+
 Diffie-Hellman load parameters from file [#1]
 dhm_file:"data_files/dhparams.pem":"9e35f430443a09904f3a39a979797d070df53378e79c2438bef4e761f3c714553328589b041c809be1d6c6b5f1fc9f47d3a25443188253a992a56818b37ba9de5a40d362e56eff0be5417474c125c199272c8fe41dea733df6f662c92ae76556e755d10c64e6a50968f67fc6ea73d0dca8569be2ba204e23580d8bca2f4975b3":"02":128
 
diff --git a/tests/suites/test_suite_mpi.data b/tests/suites/test_suite_mpi.data
index 202df1d29..90b7330a8 100644
--- a/tests/suites/test_suite_mpi.data
+++ b/tests/suites/test_suite_mpi.data
@@ -691,9 +691,12 @@ mbedtls_mpi_exp_mod:10:"-23":10:"13":10:"29":10:"":10:"5":0
 Base test mbedtls_mpi_exp_mod #5 (Negative exponent)
 mbedtls_mpi_exp_mod:10:"23":10:"-13":10:"29":10:"":10:"0":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
 
-Base test mbedtls_mpi_exp_mod #7 (Negative base + exponent)
+Base test mbedtls_mpi_exp_mod #6 (Negative base + exponent)
 mbedtls_mpi_exp_mod:10:"-23":10:"-13":10:"29":10:"":10:"0":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
 
+Base test mbedtls_mpi_exp_mod #7 (Huge exponent)
+mbedtls_mpi_exp_mod:10:"23":16:"50000000000000000000000000000000000000000000000000000000100014e4c3111300f060355040a13086f53534c00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000052b810400224ee06ec30e5753333958e280a8000000809539c2885280afd66aab21ddb8d31c6e58b8cae8b2698ef341ad29c3b45f75a7476fd5192955699a533b20b4661660341e00000040000000160000000000001604149d316d202449023f2bcb78b519bc7fffc9cbfb357c316e0603cdcdcdcd0ba34677b8b3be2c3633023100fdbfff7b67df9d7b7f7f00476fd5192955699a533b20b4661660341e00000040000000160000000000001604149d316d202449023f2bcb78b519bc7fffc9cbfb357c316e0603cdcdcdcd0ba34677b8b3be2c3633023100fdbfff7b67df9d7b7f7f000000000001000400000000000000506f6c617253530000000000000000000000000000000000000000110000f6de000000000000000000000000000000000000000000000000000000000000000000000000000000000000004c323536193017060000004f000000000000000000000005000000000000000000000000001603030039020000350303cf02020244e8786d95de3d020202e101f2f34e75c8b70a610e44c1000000000000008400000d00a30000ff60010001000016000016030102660b00026200025f00025c30820258308201c1a003020102020900fbb04c2eab109b0c300d06092a864886f70d01010505003045310b3009060355040e130241553113301106035504080c0a536f6d654853746174653121301f060355040a0c18496e7465726e6574205769646769747320507479204c7464301e170d3134303732333230353034305a170d3137303432323230353034305a3045310b3009060355042e130241553113301106035574080c0a136f6d652d53746174653121301f06035504050c18496e7465726e6574205769646769747320507479204c746430819f300d06092a864886f70d010101050003818d003081890281816602ffffff9e000000000000020000bf1400000000000100000000000000feffef00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001e1e1e001e1e1e1e1e00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000050000000000000000000000000000000000000000000000000000000000000000000000000000000000040ffd0100010000160000000000000000000000000000ff00000008000000000000000000000000000000000000000000000000000000000000000000000100014e4c3111300f060355040a13086f53534c00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000052b810400224ee06ec30e5753333958e280a8000000809539c2885280afd66aab21ddb8d31c6e58b8cae8b2698ef341ad29c3b45f75a7476fd5192955699a533b20b4661660341e00000040000000160000000000001604149d316d202449023f2bcb78b519bc7fffc9cbfb357c316e0603cdcdcdcd0ba34677b8b3be2c3633023100fdbfff7b67df9d7b7f7f00476fd5192955699a533b20b4661660341e00000040000000160000000000001604149d316d202449023f2bcb78b519bc7fffc9cbfb357c316e0603cdcdcdcd0ba34677b8b3be2c3633023100fdbfff7b67df9d7b7f7f000000000001000400000000000000506f6c617253530000000000000000000000000000000000000000110000f6de000000000000000000000000000000000000000000000000000000000000000000000000000000000000004c323536193017060000004f000000000000000000000005000000000000000000000000001603030039020000350303cf02020244e8786d95de3d020202e101f2f34e75c8b70a610e44c1000000000000008400000d00a30000ff60010001000016000016030102660b00026200025f00025c30820258308201c1a003020102020900fbb04c2eab109b0c300d06092a864886f70dc9784adc17e9e82f4cadccc1747090a92f8ca6840c0f404db671d219301706035504031310506f6c617253534c205465737420434130820122300d06092a864886f70d0101010500038201160303005b02000057030367c6699151ff4aec29cdbaabf2fbe3467cc254f81be8e78d765a2e63339fc99a2009fc99a2066310db7315864fc99a2066320db73058a3ff7f00001758e942d4abb2cdc64e9bb43ddc87c03db1b28d17e02cb23":10:"29":10:"":10:"0":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
+
 Test mbedtls_mpi_exp_mod #1
 mbedtls_mpi_exp_mod:10:"433019240910377478217373572959560109819648647016096560523769010881172869083338285573756574557395862965095016483867813043663981946477698466501451832407592327356331263124555137732393938242285782144928753919588632679050799198937132922145084847":10:"5781538327977828897150909166778407659250458379645823062042492461576758526757490910073628008613977550546382774775570888130029763571528699574717583228939535960234464230882573615930384979100379102915657483866755371559811718767760594919456971354184113721":10:"583137007797276923956891216216022144052044091311388601652961409557516421612874571554415606746479105795833145583959622117418531166391184939066520869800857530421873250114773204354963864729386957427276448683092491947566992077136553066273207777134303397724679138833126700957":10:"":10:"114597449276684355144920670007147953232659436380163461553186940113929777196018164149703566472936578890991049344459204199888254907113495794730452699842273939581048142004834330369483813876618772578869083248061616444392091693787039636316845512292127097865026290173004860736":0
 

From 16187a21bed2895747fdcdd4d03ebdcbd66f4e0b Mon Sep 17 00:00:00 2001
From: Chris Jones <christopher.jones@arm.com>
Date: Mon, 30 Nov 2020 11:16:48 +0000
Subject: [PATCH 03/11] Add ChangeLog entry for modular exponentiation size
 limit

Signed-off-by: Chris Jones <christopher.jones@arm.com>
---
 ChangeLog.d/limit_size_of_diffie_hellman_calculations.txt | 4 ++++
 1 file changed, 4 insertions(+)
 create mode 100644 ChangeLog.d/limit_size_of_diffie_hellman_calculations.txt

diff --git a/ChangeLog.d/limit_size_of_diffie_hellman_calculations.txt b/ChangeLog.d/limit_size_of_diffie_hellman_calculations.txt
new file mode 100644
index 000000000..982b7bc2c
--- /dev/null
+++ b/ChangeLog.d/limit_size_of_diffie_hellman_calculations.txt
@@ -0,0 +1,4 @@
+Security
+   * Limit the size of calculations performed by mbedtls_mpi_exp_mod to 
+     MBEDTLS_MPI_MAX_SIZE to prevent a potential denial of service when 
+     generating Diffie-Hellman key pairs. Credit to OSS-Fuzz.
\ No newline at end of file

From d10b331574f7c9349adfe185997a4ec2288845e3 Mon Sep 17 00:00:00 2001
From: Chris Jones <christopher.jones@arm.com>
Date: Wed, 2 Dec 2020 10:41:50 +0000
Subject: [PATCH 04/11] Test that overly large Diffie-Hellman keys are rejected

Adds test cases to ensure that `mbedtls_mpi_exp_mod` will return an error with
an exponent or modulus that is greater than `MBEDTLS_MPI_MAX_SIZE` in size.

Adds test cases to ensure that Diffie-Hellman will fail to make a key pair
(using `mbedtls_dhm_make_public`) when the prime modulus is greater than
`MBEDTLS_MPI_MAX_SIZE` in size.

Signed-off-by: Chris Jones <christopher.jones@arm.com>
---
 tests/suites/test_suite_dhm.data     |  7 +++++--
 tests/suites/test_suite_dhm.function | 30 +++++++++++++++++++++++++++
 tests/suites/test_suite_mpi.data     | 13 ++++++++++--
 tests/suites/test_suite_mpi.function | 31 ++++++++++++++++++++++++++++
 4 files changed, 77 insertions(+), 4 deletions(-)

diff --git a/tests/suites/test_suite_dhm.data b/tests/suites/test_suite_dhm.data
index 351ec840a..c4795b6d3 100644
--- a/tests/suites/test_suite_dhm.data
+++ b/tests/suites/test_suite_dhm.data
@@ -22,8 +22,11 @@ dhm_do_dhm:10:"3":10:"5":MBEDTLS_ERR_DHM_MAKE_PARAMS_FAILED
 Diffie-Hellman zero modulus
 dhm_do_dhm:10:"0":10:"5":MBEDTLS_ERR_DHM_BAD_INPUT_DATA
 
-Diffie-Hellman huge modulus
-dhm_do_dhm:16:"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":10:"5":MBEDTLS_ERR_DHM_MAKE_PARAMS_FAILED+MBEDTLS_ERR_MPI_BAD_INPUT_DATA
+Diffie-Hellman MPI_MAX_SIZE modulus
+dhm_make_public:MBEDTLS_MPI_MAX_SIZE:10:"5":0
+
+Diffie-Hellman MPI_MAX_SIZE + 1 modulus
+dhm_make_public:MBEDTLS_MPI_MAX_SIZE + 1:10:"5":MBEDTLS_ERR_DHM_MAKE_PUBLIC_FAILED+MBEDTLS_ERR_MPI_BAD_INPUT_DATA
 
 Diffie-Hellman load parameters from file [#1]
 dhm_file:"data_files/dhparams.pem":"9e35f430443a09904f3a39a979797d070df53378e79c2438bef4e761f3c714553328589b041c809be1d6c6b5f1fc9f47d3a25443188253a992a56818b37ba9de5a40d362e56eff0be5417474c125c199272c8fe41dea733df6f662c92ae76556e755d10c64e6a50968f67fc6ea73d0dca8569be2ba204e23580d8bca2f4975b3":"02":128
diff --git a/tests/suites/test_suite_dhm.function b/tests/suites/test_suite_dhm.function
index 0a5c61757..1726b9eb7 100644
--- a/tests/suites/test_suite_dhm.function
+++ b/tests/suites/test_suite_dhm.function
@@ -223,6 +223,36 @@ exit:
 }
 /* END_CASE */
 
+/* BEGIN_CASE */
+void dhm_make_public( int P_bytes, int radix_G, char *input_G, int result )
+{
+    mbedtls_mpi P, G;
+    mbedtls_dhm_context ctx;
+    unsigned char output[MBEDTLS_MPI_MAX_SIZE];
+
+    mbedtls_mpi_init( &P );
+    mbedtls_mpi_init( &G );
+    mbedtls_dhm_init( &ctx );
+
+    TEST_ASSERT( mbedtls_mpi_lset( &P, 1 ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_shift_l( &P, ( P_bytes * 8 ) - 1 ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_set_bit( &P, 0, 1 ) == 0 );
+
+    TEST_ASSERT( mbedtls_mpi_read_string( &G, radix_G, input_G ) == 0 );
+
+    TEST_ASSERT( mbedtls_dhm_set_group( &ctx, &P, &G ) == 0 );
+    TEST_ASSERT( mbedtls_dhm_make_public( &ctx, (int) mbedtls_mpi_size( &P ),
+                                          output, sizeof(output),
+                                          &mbedtls_test_rnd_pseudo_rand,
+                                          NULL ) == result );
+
+exit:
+    mbedtls_mpi_free( &P );
+    mbedtls_mpi_free( &G );
+    mbedtls_dhm_free( &ctx );
+}
+/* END_CASE */
+
 /* BEGIN_CASE depends_on:MBEDTLS_FS_IO */
 void dhm_file( char * filename, char * p, char * g, int len )
 {
diff --git a/tests/suites/test_suite_mpi.data b/tests/suites/test_suite_mpi.data
index 90b7330a8..aa6e0529b 100644
--- a/tests/suites/test_suite_mpi.data
+++ b/tests/suites/test_suite_mpi.data
@@ -694,8 +694,17 @@ mbedtls_mpi_exp_mod:10:"23":10:"-13":10:"29":10:"":10:"0":MBEDTLS_ERR_MPI_BAD_IN
 Base test mbedtls_mpi_exp_mod #6 (Negative base + exponent)
 mbedtls_mpi_exp_mod:10:"-23":10:"-13":10:"29":10:"":10:"0":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
 
-Base test mbedtls_mpi_exp_mod #7 (Huge exponent)
-mbedtls_mpi_exp_mod:10:"23":16:"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":10:"29":10:"":10:"0":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
+Base test mbedtls_mpi_exp_mod #7 (MAX_SIZE exponent)
+mbedtls_mpi_exp_mod_size:2:MBEDTLS_MPI_MAX_SIZE:2:10:"":0
+
+Base test mbedtls_mpi_exp_mod #8 (MAX_SIZE + 1 exponent)
+mbedtls_mpi_exp_mod_size:2:MBEDTLS_MPI_MAX_SIZE + 1:2:10:"":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
+
+Base test mbedtls_mpi_exp_mod #9 (MAX_SIZE modulus)
+mbedtls_mpi_exp_mod_size:2:2:MBEDTLS_MPI_MAX_SIZE:10:"":0
+
+Base test mbedtls_mpi_exp_mod #10 (MAX_SIZE + 1 modulus)
+mbedtls_mpi_exp_mod_size:2:2:MBEDTLS_MPI_MAX_SIZE + 1:10:"":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
 
 Test mbedtls_mpi_exp_mod #1
 mbedtls_mpi_exp_mod:10:"433019240910377478217373572959560109819648647016096560523769010881172869083338285573756574557395862965095016483867813043663981946477698466501451832407592327356331263124555137732393938242285782144928753919588632679050799198937132922145084847":10:"5781538327977828897150909166778407659250458379645823062042492461576758526757490910073628008613977550546382774775570888130029763571528699574717583228939535960234464230882573615930384979100379102915657483866755371559811718767760594919456971354184113721":10:"583137007797276923956891216216022144052044091311388601652961409557516421612874571554415606746479105795833145583959622117418531166391184939066520869800857530421873250114773204354963864729386957427276448683092491947566992077136553066273207777134303397724679138833126700957":10:"":10:"114597449276684355144920670007147953232659436380163461553186940113929777196018164149703566472936578890991049344459204199888254907113495794730452699842273939581048142004834330369483813876618772578869083248061616444392091693787039636316845512292127097865026290173004860736":0
diff --git a/tests/suites/test_suite_mpi.function b/tests/suites/test_suite_mpi.function
index e54aaffe6..97107c211 100644
--- a/tests/suites/test_suite_mpi.function
+++ b/tests/suites/test_suite_mpi.function
@@ -1164,6 +1164,37 @@ exit:
 }
 /* END_CASE */
 
+/* BEGIN_CASE */
+void mbedtls_mpi_exp_mod_size( int A_bytes, int E_bytes, int N_bytes,
+                               int radix_RR, char * input_RR, int div_result )
+{
+    mbedtls_mpi A, E, N, RR, Z;
+    mbedtls_mpi_init( &A  ); mbedtls_mpi_init( &E ); mbedtls_mpi_init( &N );
+    mbedtls_mpi_init( &RR ); mbedtls_mpi_init( &Z );
+
+    TEST_ASSERT( mbedtls_mpi_lset( &A, 1 ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_lset( &E, 1 ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_lset( &N, 1 ) == 0 );
+
+    TEST_ASSERT( mbedtls_mpi_shift_l( &A, ( A_bytes * 8 ) - 1 ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_shift_l( &E, ( E_bytes * 8 ) - 1 ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_shift_l( &N, ( N_bytes * 8 ) - 1 ) == 0 );
+
+    TEST_ASSERT( mbedtls_mpi_set_bit( &A, 0, 1 ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_set_bit( &E, 0, 1 ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_set_bit( &N, 0, 1 ) == 0 );
+
+    if( strlen( input_RR ) )
+        TEST_ASSERT( mbedtls_mpi_read_string( &RR, radix_RR, input_RR ) == 0 );
+
+    TEST_ASSERT( mbedtls_mpi_exp_mod( &Z, &A, &E, &N, &RR ) == div_result );
+
+exit:
+    mbedtls_mpi_free( &A  ); mbedtls_mpi_free( &E ); mbedtls_mpi_free( &N );
+    mbedtls_mpi_free( &RR ); mbedtls_mpi_free( &Z );
+}
+/* END_CASE */
+
 /* BEGIN_CASE */
 void mbedtls_mpi_inv_mod( int radix_X, char * input_X, int radix_Y,
                           char * input_Y, int radix_A, char * input_A,

From a03f56fe8fb8cc72fc42106993c7679aab2efe1d Mon Sep 17 00:00:00 2001
From: Chris Jones <christopher.jones@arm.com>
Date: Wed, 2 Dec 2020 16:27:42 +0000
Subject: [PATCH 05/11] Extend exponentiation test coverage

Add two further boundary tests for cases where both the exponent and modulus to
`mbedtls_mpi_exp_mod()` are `MBEDTLS_MPI_MAX_SIZE`, or longer, bytes long.

Signed-off-by: Chris Jones <christopher.jones@arm.com>
---
 tests/suites/test_suite_mpi.data | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tests/suites/test_suite_mpi.data b/tests/suites/test_suite_mpi.data
index aa6e0529b..18082330a 100644
--- a/tests/suites/test_suite_mpi.data
+++ b/tests/suites/test_suite_mpi.data
@@ -706,6 +706,12 @@ mbedtls_mpi_exp_mod_size:2:2:MBEDTLS_MPI_MAX_SIZE:10:"":0
 Base test mbedtls_mpi_exp_mod #10 (MAX_SIZE + 1 modulus)
 mbedtls_mpi_exp_mod_size:2:2:MBEDTLS_MPI_MAX_SIZE + 1:10:"":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
 
+Base test mbedtls_mpi_exp_mod #11 (MAX_SIZE exponent and modulus)
+mbedtls_mpi_exp_mod_size:2:MBEDTLS_MPI_MAX_SIZE:MBEDTLS_MPI_MAX_SIZE:10:"":0
+
+Base test mbedtls_mpi_exp_mod #12 (MAX_SIZE + 1 exponent and modulus)
+mbedtls_mpi_exp_mod_size:2:MBEDTLS_MPI_MAX_SIZE + 1:MBEDTLS_MPI_MAX_SIZE + 1:10:"":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
+
 Test mbedtls_mpi_exp_mod #1
 mbedtls_mpi_exp_mod:10:"433019240910377478217373572959560109819648647016096560523769010881172869083338285573756574557395862965095016483867813043663981946477698466501451832407592327356331263124555137732393938242285782144928753919588632679050799198937132922145084847":10:"5781538327977828897150909166778407659250458379645823062042492461576758526757490910073628008613977550546382774775570888130029763571528699574717583228939535960234464230882573615930384979100379102915657483866755371559811718767760594919456971354184113721":10:"583137007797276923956891216216022144052044091311388601652961409557516421612874571554415606746479105795833145583959622117418531166391184939066520869800857530421873250114773204354963864729386957427276448683092491947566992077136553066273207777134303397724679138833126700957":10:"":10:"114597449276684355144920670007147953232659436380163461553186940113929777196018164149703566472936578890991049344459204199888254907113495794730452699842273939581048142004834330369483813876618772578869083248061616444392091693787039636316845512292127097865026290173004860736":0
 

From aa850cdfdc6c19f6cd96cf68d55cc0b1c9e9ef09 Mon Sep 17 00:00:00 2001
From: Chris Jones <christopher.jones@arm.com>
Date: Thu, 3 Dec 2020 11:35:41 +0000
Subject: [PATCH 06/11] Reword test cases

Reword test cases to be easier to read and understand.
Adds comments to better explain what the test is doing.

Signed-off-by: Chris Jones <christopher.jones@arm.com>
---
 tests/suites/test_suite_mpi.data     | 12 ++++++------
 tests/suites/test_suite_mpi.function | 19 +++++++++++--------
 2 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/tests/suites/test_suite_mpi.data b/tests/suites/test_suite_mpi.data
index 18082330a..1c0661f4e 100644
--- a/tests/suites/test_suite_mpi.data
+++ b/tests/suites/test_suite_mpi.data
@@ -694,22 +694,22 @@ mbedtls_mpi_exp_mod:10:"23":10:"-13":10:"29":10:"":10:"0":MBEDTLS_ERR_MPI_BAD_IN
 Base test mbedtls_mpi_exp_mod #6 (Negative base + exponent)
 mbedtls_mpi_exp_mod:10:"-23":10:"-13":10:"29":10:"":10:"0":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
 
-Base test mbedtls_mpi_exp_mod #7 (MAX_SIZE exponent)
+Test mbedtls_mpi_exp_mod: MAX_SIZE exponent
 mbedtls_mpi_exp_mod_size:2:MBEDTLS_MPI_MAX_SIZE:2:10:"":0
 
-Base test mbedtls_mpi_exp_mod #8 (MAX_SIZE + 1 exponent)
+Test mbedtls_mpi_exp_mod: MAX_SIZE + 1 exponent
 mbedtls_mpi_exp_mod_size:2:MBEDTLS_MPI_MAX_SIZE + 1:2:10:"":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
 
-Base test mbedtls_mpi_exp_mod #9 (MAX_SIZE modulus)
+Test mbedtls_mpi_exp_mod: MAX_SIZE modulus
 mbedtls_mpi_exp_mod_size:2:2:MBEDTLS_MPI_MAX_SIZE:10:"":0
 
-Base test mbedtls_mpi_exp_mod #10 (MAX_SIZE + 1 modulus)
+Test mbedtls_mpi_exp_mod: MAX_SIZE + 1 modulus
 mbedtls_mpi_exp_mod_size:2:2:MBEDTLS_MPI_MAX_SIZE + 1:10:"":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
 
-Base test mbedtls_mpi_exp_mod #11 (MAX_SIZE exponent and modulus)
+Test mbedtls_mpi_exp_mod: MAX_SIZE exponent and modulus
 mbedtls_mpi_exp_mod_size:2:MBEDTLS_MPI_MAX_SIZE:MBEDTLS_MPI_MAX_SIZE:10:"":0
 
-Base test mbedtls_mpi_exp_mod #12 (MAX_SIZE + 1 exponent and modulus)
+Test mbedtls_mpi_exp_mod: MAX_SIZE + 1 exponent and modulus
 mbedtls_mpi_exp_mod_size:2:MBEDTLS_MPI_MAX_SIZE + 1:MBEDTLS_MPI_MAX_SIZE + 1:10:"":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
 
 Test mbedtls_mpi_exp_mod #1
diff --git a/tests/suites/test_suite_mpi.function b/tests/suites/test_suite_mpi.function
index 97107c211..6f305e9cf 100644
--- a/tests/suites/test_suite_mpi.function
+++ b/tests/suites/test_suite_mpi.function
@@ -1166,28 +1166,31 @@ exit:
 
 /* BEGIN_CASE */
 void mbedtls_mpi_exp_mod_size( int A_bytes, int E_bytes, int N_bytes,
-                               int radix_RR, char * input_RR, int div_result )
+                               int radix_RR, char * input_RR, int exp_result )
 {
     mbedtls_mpi A, E, N, RR, Z;
     mbedtls_mpi_init( &A  ); mbedtls_mpi_init( &E ); mbedtls_mpi_init( &N );
     mbedtls_mpi_init( &RR ); mbedtls_mpi_init( &Z );
 
+    /* Set A to 2^(A_bytes - 1) + 1 */
     TEST_ASSERT( mbedtls_mpi_lset( &A, 1 ) == 0 );
-    TEST_ASSERT( mbedtls_mpi_lset( &E, 1 ) == 0 );
-    TEST_ASSERT( mbedtls_mpi_lset( &N, 1 ) == 0 );
-
     TEST_ASSERT( mbedtls_mpi_shift_l( &A, ( A_bytes * 8 ) - 1 ) == 0 );
-    TEST_ASSERT( mbedtls_mpi_shift_l( &E, ( E_bytes * 8 ) - 1 ) == 0 );
-    TEST_ASSERT( mbedtls_mpi_shift_l( &N, ( N_bytes * 8 ) - 1 ) == 0 );
-
     TEST_ASSERT( mbedtls_mpi_set_bit( &A, 0, 1 ) == 0 );
+
+    /* Set E to 2^(E_bytes - 1) + 1 */
+    TEST_ASSERT( mbedtls_mpi_lset( &E, 1 ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_shift_l( &E, ( E_bytes * 8 ) - 1 ) == 0 );
     TEST_ASSERT( mbedtls_mpi_set_bit( &E, 0, 1 ) == 0 );
+
+    /* Set N to 2^(N_bytes - 1) + 1 */
+    TEST_ASSERT( mbedtls_mpi_lset( &N, 1 ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_shift_l( &N, ( N_bytes * 8 ) - 1 ) == 0 );
     TEST_ASSERT( mbedtls_mpi_set_bit( &N, 0, 1 ) == 0 );
 
     if( strlen( input_RR ) )
         TEST_ASSERT( mbedtls_mpi_read_string( &RR, radix_RR, input_RR ) == 0 );
 
-    TEST_ASSERT( mbedtls_mpi_exp_mod( &Z, &A, &E, &N, &RR ) == div_result );
+    TEST_ASSERT( mbedtls_mpi_exp_mod( &Z, &A, &E, &N, &RR ) == exp_result );
 
 exit:
     mbedtls_mpi_free( &A  ); mbedtls_mpi_free( &E ); mbedtls_mpi_free( &N );

From e146bdcff9ea79896a07cec30508c98f3466b258 Mon Sep 17 00:00:00 2001
From: Chris Jones <christopher.jones@arm.com>
Date: Thu, 3 Dec 2020 11:52:40 +0000
Subject: [PATCH 07/11] Fix cases where exponentiation was not fully tested

In two test cases, the exponentiation computation was not being fully tested
as when A_bytes (the base) == N_bytes (the modulus) -> A = N. When this is the
case A is reduced to 0 and therefore the result of the computation will always
be 0.

This fixes that issue and therefore increases the test coverage to ensure
different computations are actually being run.

Signed-off-by: Chris Jones <christopher.jones@arm.com>
---
 tests/suites/test_suite_mpi.data | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tests/suites/test_suite_mpi.data b/tests/suites/test_suite_mpi.data
index 1c0661f4e..e01e995ab 100644
--- a/tests/suites/test_suite_mpi.data
+++ b/tests/suites/test_suite_mpi.data
@@ -695,10 +695,10 @@ Base test mbedtls_mpi_exp_mod #6 (Negative base + exponent)
 mbedtls_mpi_exp_mod:10:"-23":10:"-13":10:"29":10:"":10:"0":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
 
 Test mbedtls_mpi_exp_mod: MAX_SIZE exponent
-mbedtls_mpi_exp_mod_size:2:MBEDTLS_MPI_MAX_SIZE:2:10:"":0
+mbedtls_mpi_exp_mod_size:2:MBEDTLS_MPI_MAX_SIZE:10:10:"":0
 
 Test mbedtls_mpi_exp_mod: MAX_SIZE + 1 exponent
-mbedtls_mpi_exp_mod_size:2:MBEDTLS_MPI_MAX_SIZE + 1:2:10:"":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
+mbedtls_mpi_exp_mod_size:2:MBEDTLS_MPI_MAX_SIZE + 1:10:10:"":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
 
 Test mbedtls_mpi_exp_mod: MAX_SIZE modulus
 mbedtls_mpi_exp_mod_size:2:2:MBEDTLS_MPI_MAX_SIZE:10:"":0

From 4592bd8982961ec466915c98f70eb569764b668a Mon Sep 17 00:00:00 2001
From: Chris Jones <christopher.jones@arm.com>
Date: Thu, 3 Dec 2020 14:24:33 +0000
Subject: [PATCH 08/11] Fix broken testing on numbers that may be greater than
 MPI_MAX_SIZE

Previously `mbedtls_mpi_exp_mod` was tested with values that were over
`MBEDTLS_MPI_MAX_SIZE` in size. This is useful to do as some paths are only
taken when the exponent is large enough however, on builds where
`MBEDTLS_MPI_MAX_SIZE` is under the size of these test values.

This fix turns off these tests when `MBEDTLS_MPI_MAX_SIZE` is too small to
safely test (notably this is the case in config-thread.h).

Signed-off-by: Chris Jones <christopher.jones@arm.com>
---
 tests/suites/test_suite_mpi.function | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/tests/suites/test_suite_mpi.function b/tests/suites/test_suite_mpi.function
index 6f305e9cf..f44db7022 100644
--- a/tests/suites/test_suite_mpi.function
+++ b/tests/suites/test_suite_mpi.function
@@ -1,6 +1,10 @@
 /* BEGIN_HEADER */
 #include "mbedtls/bignum.h"
 
+#if MBEDTLS_MPI_MAX_BITS > 256
+#define MPI_MAX_BITS_LARGER_THAN_256
+#endif
+
 typedef struct mbedtls_test_mpi_random
 {
     data_t *data;
@@ -1132,7 +1136,7 @@ exit:
 }
 /* END_CASE */
 
-/* BEGIN_CASE */
+/* BEGIN_CASE depends_on:MPI_MAX_BITS_LARGER_THAN_256 */
 void mbedtls_mpi_exp_mod( int radix_A, char * input_A, int radix_E,
                           char * input_E, int radix_N, char * input_N,
                           int radix_RR, char * input_RR, int radix_X,

From 7c430305e36e5a56eaaa06cfa2035b4493b86dac Mon Sep 17 00:00:00 2001
From: Chris Jones <christopher.jones@arm.com>
Date: Thu, 3 Dec 2020 15:22:25 +0000
Subject: [PATCH 09/11] Move dependancy to specific test cases

Move dependancy on `MBEDTLS_MPI_MAX_BITS` to apply to the specific test cases
which will break when `MBEDTLS_MPI_MAX_BITS` is too small. This re-enables
previous tests that were turned off accidentally.

Signed-off-by: Chris Jones <christopher.jones@arm.com>
---
 tests/suites/test_suite_mpi.data     | 2 ++
 tests/suites/test_suite_mpi.function | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/tests/suites/test_suite_mpi.data b/tests/suites/test_suite_mpi.data
index e01e995ab..a8fc104a1 100644
--- a/tests/suites/test_suite_mpi.data
+++ b/tests/suites/test_suite_mpi.data
@@ -713,12 +713,14 @@ Test mbedtls_mpi_exp_mod: MAX_SIZE + 1 exponent and modulus
 mbedtls_mpi_exp_mod_size:2:MBEDTLS_MPI_MAX_SIZE + 1:MBEDTLS_MPI_MAX_SIZE + 1:10:"":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
 
 Test mbedtls_mpi_exp_mod #1
+depends_on:MPI_MAX_BITS_LARGER_THAN_256
 mbedtls_mpi_exp_mod:10:"433019240910377478217373572959560109819648647016096560523769010881172869083338285573756574557395862965095016483867813043663981946477698466501451832407592327356331263124555137732393938242285782144928753919588632679050799198937132922145084847":10:"5781538327977828897150909166778407659250458379645823062042492461576758526757490910073628008613977550546382774775570888130029763571528699574717583228939535960234464230882573615930384979100379102915657483866755371559811718767760594919456971354184113721":10:"583137007797276923956891216216022144052044091311388601652961409557516421612874571554415606746479105795833145583959622117418531166391184939066520869800857530421873250114773204354963864729386957427276448683092491947566992077136553066273207777134303397724679138833126700957":10:"":10:"114597449276684355144920670007147953232659436380163461553186940113929777196018164149703566472936578890991049344459204199888254907113495794730452699842273939581048142004834330369483813876618772578869083248061616444392091693787039636316845512292127097865026290173004860736":0
 
 Test mbedtls_mpi_exp_mod (Negative base) [#1]
 mbedtls_mpi_exp_mod:10:"-10000000000":10:"10000000000":10:"99999":10:"":10:"1":0
 
 Test mbedtls_mpi_exp_mod (Negative base) [#2]
+depends_on:MPI_MAX_BITS_LARGER_THAN_256
 mbedtls_mpi_exp_mod:16:"-9f13012cd92aa72fb86ac8879d2fde4f7fd661aaae43a00971f081cc60ca277059d5c37e89652e2af2585d281d66ef6a9d38a117e9608e9e7574cd142dc55278838a2161dd56db9470d4c1da2d5df15a908ee2eb886aaa890f23be16de59386663a12f1afbb325431a3e835e3fd89b98b96a6f77382f458ef9a37e1f84a03045c8676ab55291a94c2228ea15448ee96b626b998":16:"40a54d1b9e86789f06d9607fb158672d64867665c73ee9abb545fc7a785634b354c7bae5b962ce8040cf45f2c1f3d3659b2ee5ede17534c8fc2ec85c815e8df1fe7048d12c90ee31b88a68a081f17f0d8ce5f4030521e9400083bcea73a429031d4ca7949c2000d597088e0c39a6014d8bf962b73bb2e8083bd0390a4e00b9b3":16:"eeaf0ab9adb38dd69c33f80afa8fc5e86072618775ff3c0b9ea2314c9c256576d674df7496ea81d3383b4813d692c6e0e0d5d8e250b98be48e495c1d6089dad15dc7d7b46154d6b6ce8ef4ad69b15d4982559b297bcf1885c529f566660e57ec68edbc3c05726cc02fd4cbf4976eaa9afd5138fe8376435b9fc61d2fc0eb06e3":16:"":16:"21acc7199e1b90f9b4844ffe12c19f00ec548c5d32b21c647d48b6015d8eb9ec9db05b4f3d44db4227a2b5659c1a7cceb9d5fa8fa60376047953ce7397d90aaeb7465e14e820734f84aa52ad0fc66701bcbb991d57715806a11531268e1e83dd48288c72b424a6287e9ce4e5cc4db0dd67614aecc23b0124a5776d36e5c89483":0
 
 Base test GCD #1
diff --git a/tests/suites/test_suite_mpi.function b/tests/suites/test_suite_mpi.function
index f44db7022..a16e4db17 100644
--- a/tests/suites/test_suite_mpi.function
+++ b/tests/suites/test_suite_mpi.function
@@ -1136,7 +1136,7 @@ exit:
 }
 /* END_CASE */
 
-/* BEGIN_CASE depends_on:MPI_MAX_BITS_LARGER_THAN_256 */
+/* BEGIN_CASE */
 void mbedtls_mpi_exp_mod( int radix_A, char * input_A, int radix_E,
                           char * input_E, int radix_N, char * input_N,
                           int radix_RR, char * input_RR, int radix_X,

From add99487848f9d3f5e437a4a3013a348fc1ec41b Mon Sep 17 00:00:00 2001
From: Chris Jones <christopher.jones@arm.com>
Date: Thu, 3 Dec 2020 15:45:29 +0000
Subject: [PATCH 10/11] Fix whitespace in changelog entry

Extra whitespace and a missing newline at end of file was causing an error with
`check_files.py`.

Signed-off-by: Chris Jones <christopher.jones@arm.com>
---
 ChangeLog.d/limit_size_of_diffie_hellman_calculations.txt | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/ChangeLog.d/limit_size_of_diffie_hellman_calculations.txt b/ChangeLog.d/limit_size_of_diffie_hellman_calculations.txt
index 982b7bc2c..2ba98d541 100644
--- a/ChangeLog.d/limit_size_of_diffie_hellman_calculations.txt
+++ b/ChangeLog.d/limit_size_of_diffie_hellman_calculations.txt
@@ -1,4 +1,4 @@
 Security
-   * Limit the size of calculations performed by mbedtls_mpi_exp_mod to 
-     MBEDTLS_MPI_MAX_SIZE to prevent a potential denial of service when 
-     generating Diffie-Hellman key pairs. Credit to OSS-Fuzz.
\ No newline at end of file
+   * Limit the size of calculations performed by mbedtls_mpi_exp_mod to
+     MBEDTLS_MPI_MAX_SIZE to prevent a potential denial of service when
+     generating Diffie-Hellman key pairs. Credit to OSS-Fuzz.

From e64a46f4662f7d3d2ab0f9426be9f7ef3d00f25e Mon Sep 17 00:00:00 2001
From: Chris Jones <christopher.jones@arm.com>
Date: Thu, 3 Dec 2020 17:44:03 +0000
Subject: [PATCH 11/11] Fix exponentiation tests with `MBEDTLS_MPI_MAX_BITS`
 larger than 256

Fixes an issue where configs that had `MBEDTLS_MPI_MAX_BITS` greater than 256
but smaller than the test that was running (792 bits) the test would fail
incorrectly.

Signed-off-by: Chris Jones <christopher.jones@arm.com>
---
 tests/suites/test_suite_mpi.data     | 4 ++--
 tests/suites/test_suite_mpi.function | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/tests/suites/test_suite_mpi.data b/tests/suites/test_suite_mpi.data
index a8fc104a1..d8f582df6 100644
--- a/tests/suites/test_suite_mpi.data
+++ b/tests/suites/test_suite_mpi.data
@@ -713,14 +713,14 @@ Test mbedtls_mpi_exp_mod: MAX_SIZE + 1 exponent and modulus
 mbedtls_mpi_exp_mod_size:2:MBEDTLS_MPI_MAX_SIZE + 1:MBEDTLS_MPI_MAX_SIZE + 1:10:"":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
 
 Test mbedtls_mpi_exp_mod #1
-depends_on:MPI_MAX_BITS_LARGER_THAN_256
+depends_on:MPI_MAX_BITS_LARGER_THAN_792
 mbedtls_mpi_exp_mod:10:"433019240910377478217373572959560109819648647016096560523769010881172869083338285573756574557395862965095016483867813043663981946477698466501451832407592327356331263124555137732393938242285782144928753919588632679050799198937132922145084847":10:"5781538327977828897150909166778407659250458379645823062042492461576758526757490910073628008613977550546382774775570888130029763571528699574717583228939535960234464230882573615930384979100379102915657483866755371559811718767760594919456971354184113721":10:"583137007797276923956891216216022144052044091311388601652961409557516421612874571554415606746479105795833145583959622117418531166391184939066520869800857530421873250114773204354963864729386957427276448683092491947566992077136553066273207777134303397724679138833126700957":10:"":10:"114597449276684355144920670007147953232659436380163461553186940113929777196018164149703566472936578890991049344459204199888254907113495794730452699842273939581048142004834330369483813876618772578869083248061616444392091693787039636316845512292127097865026290173004860736":0
 
 Test mbedtls_mpi_exp_mod (Negative base) [#1]
 mbedtls_mpi_exp_mod:10:"-10000000000":10:"10000000000":10:"99999":10:"":10:"1":0
 
 Test mbedtls_mpi_exp_mod (Negative base) [#2]
-depends_on:MPI_MAX_BITS_LARGER_THAN_256
+depends_on:MPI_MAX_BITS_LARGER_THAN_792
 mbedtls_mpi_exp_mod:16:"-9f13012cd92aa72fb86ac8879d2fde4f7fd661aaae43a00971f081cc60ca277059d5c37e89652e2af2585d281d66ef6a9d38a117e9608e9e7574cd142dc55278838a2161dd56db9470d4c1da2d5df15a908ee2eb886aaa890f23be16de59386663a12f1afbb325431a3e835e3fd89b98b96a6f77382f458ef9a37e1f84a03045c8676ab55291a94c2228ea15448ee96b626b998":16:"40a54d1b9e86789f06d9607fb158672d64867665c73ee9abb545fc7a785634b354c7bae5b962ce8040cf45f2c1f3d3659b2ee5ede17534c8fc2ec85c815e8df1fe7048d12c90ee31b88a68a081f17f0d8ce5f4030521e9400083bcea73a429031d4ca7949c2000d597088e0c39a6014d8bf962b73bb2e8083bd0390a4e00b9b3":16:"eeaf0ab9adb38dd69c33f80afa8fc5e86072618775ff3c0b9ea2314c9c256576d674df7496ea81d3383b4813d692c6e0e0d5d8e250b98be48e495c1d6089dad15dc7d7b46154d6b6ce8ef4ad69b15d4982559b297bcf1885c529f566660e57ec68edbc3c05726cc02fd4cbf4976eaa9afd5138fe8376435b9fc61d2fc0eb06e3":16:"":16:"21acc7199e1b90f9b4844ffe12c19f00ec548c5d32b21c647d48b6015d8eb9ec9db05b4f3d44db4227a2b5659c1a7cceb9d5fa8fa60376047953ce7397d90aaeb7465e14e820734f84aa52ad0fc66701bcbb991d57715806a11531268e1e83dd48288c72b424a6287e9ce4e5cc4db0dd67614aecc23b0124a5776d36e5c89483":0
 
 Base test GCD #1
diff --git a/tests/suites/test_suite_mpi.function b/tests/suites/test_suite_mpi.function
index a16e4db17..4fb447f9c 100644
--- a/tests/suites/test_suite_mpi.function
+++ b/tests/suites/test_suite_mpi.function
@@ -1,8 +1,8 @@
 /* BEGIN_HEADER */
 #include "mbedtls/bignum.h"
 
-#if MBEDTLS_MPI_MAX_BITS > 256
-#define MPI_MAX_BITS_LARGER_THAN_256
+#if MBEDTLS_MPI_MAX_BITS > 792
+#define MPI_MAX_BITS_LARGER_THAN_792
 #endif
 
 typedef struct mbedtls_test_mpi_random