CR50: enable the bignum library to handle word un-aligned keys

The TPM2 api does not require keys to be word-aligned,
so have the compiler generate alignment-safe reads where
necessary.

BRANCH=none
BUG=chrome-os-partner:43025,chrome-os-partner:47524
TEST=tests under test/tpm2/ pass, more TCG tests pass.

Change-Id: I247e29f2bec139ab7ed4010ffb58cdae77ba9e0b
Signed-off-by: nagendra modadugu <ngm@google.com>
Reviewed-on: https://chromium-review.googlesource.com/326201
Commit-Ready: Nagendra Modadugu <ngm@google.com>
Tested-by: Nagendra Modadugu <ngm@google.com>
Reviewed-by: Vadim Bendebury <vbendeb@chromium.org>

4 files changed, 135 insertions, 147 deletions

diff --git a/board/cr50/tpm2/rsa.c b/board/cr50/tpm2/rsa.c
index dfc996bca4..b31a5012fb 100644
--- a/board/cr50/tpm2/rsa.c
+++ b/board/cr50/tpm2/rsa.c
@@ -74,7 +74,7 @@ CRYPT_RESULT _cpri__EncryptRSA(uint32_t *out_len, uint8_t *out,
 
 	rsa.e = key->exponent;
 	rsa.N.dmax = key->publicKey->size / sizeof(uint32_t);
-	rsa.N.d = (uint32_t *) &key->publicKey->buffer;
+	rsa.N.d = (struct access_helper *) &key->publicKey->buffer;
 	rsa.d.dmax = 0;
 	rsa.d.d = NULL;
 
@@ -101,9 +101,9 @@ CRYPT_RESULT _cpri__DecryptRSA(uint32_t *out_len, uint8_t *out,
 
 	rsa.e = key->exponent;
 	rsa.N.dmax = key->publicKey->size / sizeof(uint32_t);
-	rsa.N.d = (uint32_t *) &key->publicKey->buffer;
+	rsa.N.d = (struct access_helper *) &key->publicKey->buffer;
 	rsa.d.dmax = key->privateKey->size / sizeof(uint32_t);
-	rsa.d.d = (uint32_t *) &key->privateKey->buffer;
+	rsa.d.d = (struct access_helper *) &key->privateKey->buffer;
 
 	if (DCRYPTO_rsa_decrypt(&rsa, out, out_len, in, in_len, padding,
 					hashing, label))
@@ -127,9 +127,9 @@ CRYPT_RESULT _cpri__SignRSA(uint32_t *out_len, uint8_t *out,
 
 	rsa.e = key->exponent;
 	rsa.N.dmax = key->publicKey->size / sizeof(uint32_t);
-	rsa.N.d = (uint32_t *) &key->publicKey->buffer;
+	rsa.N.d = (struct access_helper *) &key->publicKey->buffer;
 	rsa.d.dmax = key->privateKey->size / sizeof(uint32_t);
-	rsa.d.d = (uint32_t *) &key->privateKey->buffer;
+	rsa.d.d = (struct access_helper *) &key->privateKey->buffer;
 
 	if (DCRYPTO_rsa_sign(&rsa, out, out_len, in, in_len, padding, hashing))
 		return CRYPT_SUCCESS;
@@ -153,7 +153,7 @@ CRYPT_RESULT _cpri__ValidateSignatureRSA(
 
 	rsa.e = key->exponent;
 	rsa.N.dmax = key->publicKey->size / sizeof(uint32_t);
-	rsa.N.d = (uint32_t *) &key->publicKey->buffer;
+	rsa.N.d = (struct access_helper *) &key->publicKey->buffer;
 	rsa.d.dmax = 0;
 	rsa.d.d = NULL;
 
@@ -176,136 +176,123 @@ enum {
 	TEST_RSA_KEYGEN = 4
 };
 
-struct TPM2B_aligned {
-	uint16_t pad;
-	TPM2B_PUBLIC_KEY_RSA bn;
-} __packed __aligned(4);
-
-static const struct TPM2B_aligned RSA_768_N = {
-	.bn = {
-		.t = {96, {
-				0x69, 0x85, 0x39, 0x2d, 0x78, 0x2b, 0x90, 0x75,
-				0xe1, 0x7c, 0xc1, 0x7b, 0xbd, 0x5b, 0xdd, 0xfd,
-				0x00, 0x36, 0xf7, 0x38, 0x74, 0x33, 0x2b, 0xa8,
-				0x53, 0x89, 0x10, 0xa7, 0x2d, 0x3c, 0xe6, 0x00,
-				0xa3, 0xe5, 0x8b, 0x5f, 0xed, 0x77, 0x32, 0xc0,
-				0x0f, 0xe2, 0x2c, 0x51, 0x1b, 0x46, 0xba, 0x18,
-				0xc0, 0x4e, 0x1b, 0x44, 0xdf, 0x94, 0xcc, 0x15,
-				0xe1, 0x67, 0x48, 0x3a, 0x12, 0xc4, 0x0c, 0x82,
-				0xd2, 0xfa, 0xfe, 0x74, 0x6e, 0x49, 0xa4, 0x8b,
-				0x64, 0xc2, 0x3b, 0x33, 0x36, 0x72, 0x24, 0xdb,
-				0x17, 0x86, 0x5a, 0x35, 0xd2, 0x23, 0x20, 0xd4,
-				0x7c, 0xf0, 0x32, 0xd9, 0x46, 0xed, 0xdb, 0xb0
-			}
+static const TPM2B_PUBLIC_KEY_RSA RSA_768_N = {
+	.t = {96, {
+			0x69, 0x85, 0x39, 0x2d, 0x78, 0x2b, 0x90, 0x75,
+			0xe1, 0x7c, 0xc1, 0x7b, 0xbd, 0x5b, 0xdd, 0xfd,
+			0x00, 0x36, 0xf7, 0x38, 0x74, 0x33, 0x2b, 0xa8,
+			0x53, 0x89, 0x10, 0xa7, 0x2d, 0x3c, 0xe6, 0x00,
+			0xa3, 0xe5, 0x8b, 0x5f, 0xed, 0x77, 0x32, 0xc0,
+			0x0f, 0xe2, 0x2c, 0x51, 0x1b, 0x46, 0xba, 0x18,
+			0xc0, 0x4e, 0x1b, 0x44, 0xdf, 0x94, 0xcc, 0x15,
+			0xe1, 0x67, 0x48, 0x3a, 0x12, 0xc4, 0x0c, 0x82,
+			0xd2, 0xfa, 0xfe, 0x74, 0x6e, 0x49, 0xa4, 0x8b,
+			0x64, 0xc2, 0x3b, 0x33, 0x36, 0x72, 0x24, 0xdb,
+			0x17, 0x86, 0x5a, 0x35, 0xd2, 0x23, 0x20, 0xd4,
+			0x7c, 0xf0, 0x32, 0xd9, 0x46, 0xed, 0xdb, 0xb0
 		}
 	}
 };
 
-static const struct TPM2B_aligned RSA_768_D = {
-	.bn = {
-		.t = {96, {
-				0x01, 0x40, 0x76, 0x7b, 0x41, 0xd6, 0xd9, 0x17,
-				0xfe, 0x52, 0x6d, 0xdd, 0x24, 0x70, 0xbc, 0x97,
-				0x7e, 0xcf, 0x54, 0x22, 0x4c, 0x71, 0x29, 0xf5,
-				0xb2, 0xe2, 0xf6, 0xf8, 0x8b, 0x9e, 0x20, 0x1a,
-				0x1e, 0x67, 0xee, 0x59, 0xf9, 0x83, 0x6b, 0x91,
-				0x8d, 0xdf, 0x03, 0xfc, 0xdd, 0x0f, 0x35, 0xd7,
-				0xa2, 0x5d, 0x06, 0x3f, 0x45, 0xb9, 0xb0, 0x23,
-				0x90, 0x7b, 0x11, 0x32, 0xc1, 0xf2, 0x12, 0xdb,
-				0x61, 0xf9, 0xa7, 0x31, 0x24, 0xc8, 0x66, 0x4e,
-				0x49, 0x72, 0xb9, 0xce, 0xa6, 0x5b, 0xab, 0x46,
-				0x45, 0xdf, 0x75, 0x76, 0x3e, 0xd3, 0x42, 0x9f,
-				0x5c, 0x1b, 0x8c, 0x25, 0x50, 0xb9, 0xad, 0xae
-			}
+static const TPM2B_PUBLIC_KEY_RSA RSA_768_D = {
+	.t = {96, {
+			0x01, 0x40, 0x76, 0x7b, 0x41, 0xd6, 0xd9, 0x17,
+			0xfe, 0x52, 0x6d, 0xdd, 0x24, 0x70, 0xbc, 0x97,
+			0x7e, 0xcf, 0x54, 0x22, 0x4c, 0x71, 0x29, 0xf5,
+			0xb2, 0xe2, 0xf6, 0xf8, 0x8b, 0x9e, 0x20, 0x1a,
+			0x1e, 0x67, 0xee, 0x59, 0xf9, 0x83, 0x6b, 0x91,
+			0x8d, 0xdf, 0x03, 0xfc, 0xdd, 0x0f, 0x35, 0xd7,
+			0xa2, 0x5d, 0x06, 0x3f, 0x45, 0xb9, 0xb0, 0x23,
+			0x90, 0x7b, 0x11, 0x32, 0xc1, 0xf2, 0x12, 0xdb,
+			0x61, 0xf9, 0xa7, 0x31, 0x24, 0xc8, 0x66, 0x4e,
+			0x49, 0x72, 0xb9, 0xce, 0xa6, 0x5b, 0xab, 0x46,
+			0x45, 0xdf, 0x75, 0x76, 0x3e, 0xd3, 0x42, 0x9f,
+			0x5c, 0x1b, 0x8c, 0x25, 0x50, 0xb9, 0xad, 0xae
 		}
 	}
 };
 
-static const struct TPM2B_aligned RSA_2048_N = {
-	.bn = {
-		.t = {256, {
-				0x99, 0xa9, 0x93, 0xdf, 0xe8, 0xde, 0x41, 0x07,
-				0xe9, 0xb1, 0x4f, 0x53, 0xa6, 0x11, 0xe3, 0x67,
-				0x88, 0xc5, 0x9a, 0x57, 0xa5, 0x38, 0x1f, 0x69,
-				0x51, 0xf2, 0xa7, 0xb5, 0x6a, 0xd2, 0x1a, 0xf2,
-				0x0c, 0x62, 0xad, 0x33, 0x1f, 0x82, 0x21, 0x4a,
-				0x72, 0xb3, 0x6e, 0xba, 0xfd, 0x66, 0x3e, 0xef,
-				0x40, 0x78, 0xa7, 0x37, 0x97, 0x4a, 0x74, 0x63,
-				0x23, 0x05, 0x2e, 0x55, 0x6d, 0x36, 0xd0, 0xb7,
-				0x8c, 0xb7, 0x83, 0x60, 0x3b, 0xa1, 0x58, 0x5d,
-				0xdc, 0xef, 0xf7, 0x2c, 0x5e, 0x05, 0x27, 0xbc,
-				0xb0, 0x4d, 0xc9, 0xff, 0x04, 0x50, 0x22, 0x97,
-				0xe7, 0x15, 0x66, 0xa5, 0x24, 0x0e, 0x86, 0xa6,
-				0x36, 0x9c, 0x92, 0xa2, 0x16, 0x51, 0xed, 0xc2,
-				0xea, 0xbf, 0xf4, 0xb2, 0x5e, 0x3a, 0xd7, 0xc5,
-				0xa3, 0xfa, 0xf0, 0xcf, 0xcf, 0x7b, 0xc8, 0x5c,
-				0x07, 0xe2, 0xcc, 0xa8, 0xb8, 0x36, 0x76, 0xb1,
-				0xc9, 0xbb, 0x48, 0x38, 0xbe, 0x0b, 0x57, 0xce,
-				0x05, 0x2d, 0xf1, 0xdb, 0x7b, 0x94, 0xb6, 0xcd,
-				0x3a, 0xa8, 0x50, 0x49, 0xca, 0x18, 0xb3, 0x52,
-				0x18, 0x49, 0xde, 0x10, 0xf8, 0x41, 0x40, 0x6e,
-				0x51, 0xaf, 0xdd, 0x06, 0xc3, 0x30, 0xc7, 0x57,
-				0x6b, 0xd4, 0xdc, 0x10, 0x46, 0x30, 0x04, 0x23,
-				0x98, 0xc0, 0xf0, 0xb4, 0xeb, 0x5d, 0xc9, 0x6e,
-				0x50, 0x1f, 0xd7, 0xd9, 0xac, 0xf2, 0x0d, 0x06,
-				0xe3, 0x9b, 0x5e, 0xde, 0x2a, 0xaa, 0xb1, 0xaf,
-				0xd6, 0x97, 0x68, 0x2d, 0xeb, 0x0c, 0x7b, 0x75,
-				0x49, 0x23, 0x64, 0xbe, 0x90, 0x53, 0x82, 0x99,
-				0xa2, 0x50, 0x78, 0x0c, 0x9f, 0x72, 0xc1, 0x0a,
-				0x0f, 0x32, 0x75, 0xed, 0x1f, 0x6e, 0xef, 0x2c,
-				0x2e, 0x1d, 0x4c, 0x19, 0x85, 0x5c, 0x90, 0x95,
-				0xe3, 0x4b, 0x86, 0xf5, 0xb7, 0x9f, 0x73, 0xcd,
-				0xbe, 0x15, 0x8e, 0x43, 0x2e, 0x61, 0xd7, 0x9c
-			}
+static const TPM2B_PUBLIC_KEY_RSA RSA_2048_N = {
+	.t = {256, {
+			0x99, 0xa9, 0x93, 0xdf, 0xe8, 0xde, 0x41, 0x07,
+			0xe9, 0xb1, 0x4f, 0x53, 0xa6, 0x11, 0xe3, 0x67,
+			0x88, 0xc5, 0x9a, 0x57, 0xa5, 0x38, 0x1f, 0x69,
+			0x51, 0xf2, 0xa7, 0xb5, 0x6a, 0xd2, 0x1a, 0xf2,
+			0x0c, 0x62, 0xad, 0x33, 0x1f, 0x82, 0x21, 0x4a,
+			0x72, 0xb3, 0x6e, 0xba, 0xfd, 0x66, 0x3e, 0xef,
+			0x40, 0x78, 0xa7, 0x37, 0x97, 0x4a, 0x74, 0x63,
+			0x23, 0x05, 0x2e, 0x55, 0x6d, 0x36, 0xd0, 0xb7,
+			0x8c, 0xb7, 0x83, 0x60, 0x3b, 0xa1, 0x58, 0x5d,
+			0xdc, 0xef, 0xf7, 0x2c, 0x5e, 0x05, 0x27, 0xbc,
+			0xb0, 0x4d, 0xc9, 0xff, 0x04, 0x50, 0x22, 0x97,
+			0xe7, 0x15, 0x66, 0xa5, 0x24, 0x0e, 0x86, 0xa6,
+			0x36, 0x9c, 0x92, 0xa2, 0x16, 0x51, 0xed, 0xc2,
+			0xea, 0xbf, 0xf4, 0xb2, 0x5e, 0x3a, 0xd7, 0xc5,
+			0xa3, 0xfa, 0xf0, 0xcf, 0xcf, 0x7b, 0xc8, 0x5c,
+			0x07, 0xe2, 0xcc, 0xa8, 0xb8, 0x36, 0x76, 0xb1,
+			0xc9, 0xbb, 0x48, 0x38, 0xbe, 0x0b, 0x57, 0xce,
+			0x05, 0x2d, 0xf1, 0xdb, 0x7b, 0x94, 0xb6, 0xcd,
+			0x3a, 0xa8, 0x50, 0x49, 0xca, 0x18, 0xb3, 0x52,
+			0x18, 0x49, 0xde, 0x10, 0xf8, 0x41, 0x40, 0x6e,
+			0x51, 0xaf, 0xdd, 0x06, 0xc3, 0x30, 0xc7, 0x57,
+			0x6b, 0xd4, 0xdc, 0x10, 0x46, 0x30, 0x04, 0x23,
+			0x98, 0xc0, 0xf0, 0xb4, 0xeb, 0x5d, 0xc9, 0x6e,
+			0x50, 0x1f, 0xd7, 0xd9, 0xac, 0xf2, 0x0d, 0x06,
+			0xe3, 0x9b, 0x5e, 0xde, 0x2a, 0xaa, 0xb1, 0xaf,
+			0xd6, 0x97, 0x68, 0x2d, 0xeb, 0x0c, 0x7b, 0x75,
+			0x49, 0x23, 0x64, 0xbe, 0x90, 0x53, 0x82, 0x99,
+			0xa2, 0x50, 0x78, 0x0c, 0x9f, 0x72, 0xc1, 0x0a,
+			0x0f, 0x32, 0x75, 0xed, 0x1f, 0x6e, 0xef, 0x2c,
+			0x2e, 0x1d, 0x4c, 0x19, 0x85, 0x5c, 0x90, 0x95,
+			0xe3, 0x4b, 0x86, 0xf5, 0xb7, 0x9f, 0x73, 0xcd,
+			0xbe, 0x15, 0x8e, 0x43, 0x2e, 0x61, 0xd7, 0x9c
 		}
 	}
 };
 
-static const struct TPM2B_aligned RSA_2048_D = {
-	.bn = {
-		.t  = {256, {
-				0xf5, 0x95, 0x99, 0xca, 0x31, 0x84, 0x66, 0x4c,
-				0xa9, 0x29, 0x24, 0x74, 0x22, 0x29, 0xb4, 0x64,
-				0x5b, 0x22, 0xeb, 0x5d, 0x2f, 0xe3, 0x62, 0x21,
-				0x02, 0x16, 0x33, 0x16, 0xe4, 0xad, 0x10, 0x52,
-				0x3f, 0xf0, 0xf1, 0x86, 0x68, 0x54, 0x47, 0x24,
-				0xcc, 0x5c, 0x08, 0x82, 0x0f, 0x68, 0xdd, 0x79,
-				0x55, 0x11, 0x07, 0x6d, 0x56, 0x89, 0x30, 0xf1,
-				0x7f, 0xaf, 0xb1, 0xb8, 0x41, 0xe8, 0x7a, 0x82,
-				0x03, 0x1a, 0x95, 0xd7, 0x00, 0x7c, 0xb7, 0x04,
-				0xee, 0x8e, 0x9b, 0xbc, 0x4f, 0xdf, 0xa8, 0x38,
-				0xea, 0xbf, 0xfb, 0x79, 0xa0, 0xd3, 0xd6, 0xc2,
-				0x1f, 0x67, 0xa2, 0x88, 0x2b, 0x1d, 0x23, 0xc6,
-				0x19, 0xfc, 0x27, 0x45, 0xcf, 0xbd, 0xc7, 0xe9,
-				0x6e, 0x7a, 0xe2, 0x84, 0x4c, 0x9c, 0x16, 0x65,
-				0xb0, 0xa6, 0x88, 0xc5, 0xbe, 0x30, 0x70, 0xb9,
-				0xc6, 0x6d, 0x3f, 0xf5, 0xcd, 0x52, 0x97, 0x54,
-				0x15, 0x26, 0xd2, 0x06, 0x82, 0xcc, 0xe7, 0x02,
-				0x1a, 0x23, 0xb8, 0x0a, 0x71, 0xde, 0x91, 0x82,
-				0xe4, 0x1e, 0xbe, 0x67, 0xeb, 0x94, 0x24, 0x22,
-				0xe7, 0x27, 0xfa, 0x52, 0xf2, 0x94, 0x5e, 0x6e,
-				0x85, 0xc1, 0x47, 0x42, 0xdc, 0xae, 0x8b, 0xaf,
-				0x4e, 0x32, 0xc6, 0x8d, 0xd3, 0xc0, 0xa2, 0x6b,
-				0x02, 0x96, 0x76, 0x0a, 0x96, 0x87, 0x16, 0x35,
-				0xc1, 0xea, 0xf7, 0x91, 0xa4, 0xa3, 0x1b, 0x40,
-				0xc0, 0x95, 0x20, 0x14, 0x9f, 0x32, 0xad, 0x39,
-				0x19, 0x29, 0xea, 0x80, 0x33, 0x2c, 0x31, 0x86,
-				0xca, 0x5e, 0x89, 0xf0, 0x74, 0xdf, 0x8f, 0xdc,
-				0xa3, 0xf3, 0xbe, 0x26, 0xd0, 0xa3, 0xb4, 0x7c,
-				0x6e, 0xdf, 0xad, 0xdb, 0x26, 0xf3, 0xaa, 0xfb,
-				0x68, 0x56, 0x43, 0xb9, 0x7f, 0x19, 0x70, 0x67,
-				0x5a, 0x66, 0x15, 0x6f, 0xe2, 0x14, 0x8f, 0xbc,
-				0x89, 0x8b, 0x4a, 0xdf, 0x1f, 0x02, 0x9d, 0x4e
-			}
+static const TPM2B_PUBLIC_KEY_RSA RSA_2048_D = {
+	.t  = {256, {
+			0xf5, 0x95, 0x99, 0xca, 0x31, 0x84, 0x66, 0x4c,
+			0xa9, 0x29, 0x24, 0x74, 0x22, 0x29, 0xb4, 0x64,
+			0x5b, 0x22, 0xeb, 0x5d, 0x2f, 0xe3, 0x62, 0x21,
+			0x02, 0x16, 0x33, 0x16, 0xe4, 0xad, 0x10, 0x52,
+			0x3f, 0xf0, 0xf1, 0x86, 0x68, 0x54, 0x47, 0x24,
+			0xcc, 0x5c, 0x08, 0x82, 0x0f, 0x68, 0xdd, 0x79,
+			0x55, 0x11, 0x07, 0x6d, 0x56, 0x89, 0x30, 0xf1,
+			0x7f, 0xaf, 0xb1, 0xb8, 0x41, 0xe8, 0x7a, 0x82,
+			0x03, 0x1a, 0x95, 0xd7, 0x00, 0x7c, 0xb7, 0x04,
+			0xee, 0x8e, 0x9b, 0xbc, 0x4f, 0xdf, 0xa8, 0x38,
+			0xea, 0xbf, 0xfb, 0x79, 0xa0, 0xd3, 0xd6, 0xc2,
+			0x1f, 0x67, 0xa2, 0x88, 0x2b, 0x1d, 0x23, 0xc6,
+			0x19, 0xfc, 0x27, 0x45, 0xcf, 0xbd, 0xc7, 0xe9,
+			0x6e, 0x7a, 0xe2, 0x84, 0x4c, 0x9c, 0x16, 0x65,
+			0xb0, 0xa6, 0x88, 0xc5, 0xbe, 0x30, 0x70, 0xb9,
+			0xc6, 0x6d, 0x3f, 0xf5, 0xcd, 0x52, 0x97, 0x54,
+			0x15, 0x26, 0xd2, 0x06, 0x82, 0xcc, 0xe7, 0x02,
+			0x1a, 0x23, 0xb8, 0x0a, 0x71, 0xde, 0x91, 0x82,
+			0xe4, 0x1e, 0xbe, 0x67, 0xeb, 0x94, 0x24, 0x22,
+			0xe7, 0x27, 0xfa, 0x52, 0xf2, 0x94, 0x5e, 0x6e,
+			0x85, 0xc1, 0x47, 0x42, 0xdc, 0xae, 0x8b, 0xaf,
+			0x4e, 0x32, 0xc6, 0x8d, 0xd3, 0xc0, 0xa2, 0x6b,
+			0x02, 0x96, 0x76, 0x0a, 0x96, 0x87, 0x16, 0x35,
+			0xc1, 0xea, 0xf7, 0x91, 0xa4, 0xa3, 0x1b, 0x40,
+			0xc0, 0x95, 0x20, 0x14, 0x9f, 0x32, 0xad, 0x39,
+			0x19, 0x29, 0xea, 0x80, 0x33, 0x2c, 0x31, 0x86,
+			0xca, 0x5e, 0x89, 0xf0, 0x74, 0xdf, 0x8f, 0xdc,
+			0xa3, 0xf3, 0xbe, 0x26, 0xd0, 0xa3, 0xb4, 0x7c,
+			0x6e, 0xdf, 0xad, 0xdb, 0x26, 0xf3, 0xaa, 0xfb,
+			0x68, 0x56, 0x43, 0xb9, 0x7f, 0x19, 0x70, 0x67,
+			0x5a, 0x66, 0x15, 0x6f, 0xe2, 0x14, 0x8f, 0xbc,
+			0x89, 0x8b, 0x4a, 0xdf, 0x1f, 0x02, 0x9d, 0x4e
 		}
 	}
 };
 
 static const RSA_KEY RSA_768 = {
-	65537, (TPM2B *) &RSA_768_N.bn.b, (TPM2B *) &RSA_768_D.bn.b
+	65537, (TPM2B *) &RSA_768_N.b, (TPM2B *) &RSA_768_D.b
 };
 static const RSA_KEY RSA_2048 = {
-	65537, (TPM2B *) &RSA_2048_N.bn.b, (TPM2B *) &RSA_2048_D.bn.b
+	65537, (TPM2B *) &RSA_2048_N.b, (TPM2B *) &RSA_2048_D.b
 };
 
 #define MAX_MSG_BYTES RSA_MAX_BYTES
diff --git a/chip/g/dcrypto/bn.c b/chip/g/dcrypto/bn.c
index 829d10e602..f4aaf11912 100644
--- a/chip/g/dcrypto/bn.c
+++ b/chip/g/dcrypto/bn.c
@@ -18,16 +18,14 @@ void bn_init(struct BIGNUM *b, void *buf, size_t len)
 {
 	/* Only word-multiple sized buffers accepted. */
 	assert((len & 0x3) == 0);
-	/* Only word-aligned buffers accepted. */
-	assert(((uintptr_t) buf & 0x3) == 0);
 	b->dmax = len / BN_BYTES;
 	dcrypto_memset(buf, 0x00, len);
-	b->d = (uint32_t *) buf;
+	b->d = (struct access_helper *) buf;
 }
 
 int bn_check_topbit(const struct BIGNUM *N)
 {
-	return N->d[N->dmax - 1] >> 31;
+	return BN_DIGIT(N, N->dmax - 1) >> 31;
 }
 
 /* a[n]. */
@@ -43,7 +41,7 @@ static int bn_is_bit_set(const struct BIGNUM *a, int n)
 	if (a->dmax <= i)
 		return 0;
 
-	return (a->d[i] >> j) & 1;
+	return (BN_DIGIT(a, i) >> j) & 1;
 }
 
 /* a[] >= b[]. */
@@ -52,9 +50,9 @@ static int bn_gte(const struct BIGNUM *a, const struct BIGNUM *b)
 {
 	int i;
 
-	for (i = a->dmax - 1; a->d[i] == b->d[i] && i > 0; --i)
+	for (i = a->dmax - 1; BN_DIGIT(a, i) == BN_DIGIT(b, i) && i > 0; --i)
 		;
-	return a->d[i] >= b->d[i];
+	return BN_DIGIT(a, i) >= BN_DIGIT(b, i);
 }
 
 /* c[] = c[] - a[], assumes c > a. */
@@ -64,8 +62,8 @@ static uint32_t bn_sub(struct BIGNUM *c, const struct BIGNUM *a)
 	int i;
 
 	for (i = 0; i < a->dmax; i++) {
-		A += (uint64_t) c->d[i] - a->d[i];
-		c->d[i] = (uint32_t) A;
+		A += (uint64_t) BN_DIGIT(c, i) - BN_DIGIT(a, i);
+		BN_DIGIT(c, i) = (uint32_t) A;
 		A >>= 32;
 	}
 	return (uint32_t) A;  /* 0 or -1. */
@@ -78,8 +76,8 @@ static uint32_t bn_add(struct BIGNUM *c, const struct BIGNUM *a)
 	int i;
 
 	for (i = 0; i < a->dmax; ++i) {
-		A += (uint64_t) c->d[i] + a->d[i];
-		c->d[i] = (uint32_t) A;
+		A += (uint64_t) BN_DIGIT(c, i) + BN_DIGIT(a, i);
+		BN_DIGIT(c, i) = (uint32_t) A;
 		A >>= 32;
 	}
 
@@ -94,9 +92,9 @@ static uint32_t bn_lshift(struct BIGNUM *r)
 	uint32_t carry = 0;
 
 	for (i = 0; i < r->dmax; i++) {
-		w = (r->d[i] << 1) | carry;
-		carry = r->d[i] >> 31;
-		r->d[i] = w;
+		w = (BN_DIGIT(r, i) << 1) | carry;
+		carry = BN_DIGIT(r, i) >> 31;
+		BN_DIGIT(r, i) = w;
 	}
 	return carry;
 }
@@ -113,20 +111,21 @@ static void bn_mont_mul_add(struct BIGNUM *c, const uint32_t a,
 	{
 		register uint64_t tmp;
 
-		tmp = c->d[0] + (uint64_t) a * b->d[0];
+		tmp = BN_DIGIT(c, 0) + (uint64_t) a * BN_DIGIT(b, 0);
 		A = tmp >> 32;
 		d0 = (uint32_t) tmp * (uint32_t) nprime;
-		tmp = (uint32_t)tmp + (uint64_t) d0 * N->d[0];
+		tmp = (uint32_t)tmp + (uint64_t) d0 * BN_DIGIT(N, 0);
 		B = tmp >> 32;
 	}
 
 	for (i = 0; i < N->dmax - 1;) {
 		register uint64_t tmp;
 
-		tmp = A + (uint64_t) a * b->d[i + 1] + c->d[i + 1];
+		tmp = A + (uint64_t) a * BN_DIGIT(b, i + 1) +
+			BN_DIGIT(c, i + 1);
 		A = tmp >> 32;
-		tmp = B + (uint64_t) d0 * N->d[i + 1] + (uint32_t) tmp;
-		c->d[i] = (uint32_t) tmp;
+		tmp = B + (uint64_t) d0 * BN_DIGIT(N, i + 1) + (uint32_t) tmp;
+		BN_DIGIT(c, i) = (uint32_t) tmp;
 		B = tmp >> 32;
 		++i;
 	}
@@ -134,7 +133,7 @@ static void bn_mont_mul_add(struct BIGNUM *c, const uint32_t a,
 	{
 		uint64_t tmp = (uint64_t) A + B;
 
-		c->d[i] = (uint32_t) tmp;
+		BN_DIGIT(c, i) = (uint32_t) tmp;
 		A = tmp >> 32;  /* 0 or 1. */
 		if (A)
 			bn_sub(c, N);
@@ -149,11 +148,11 @@ static void bn_mont_mul(struct BIGNUM *c, const struct BIGNUM *a,
 	int i;
 
 	for (i = 0; i < N->dmax; i++)
-		c->d[i] = 0;
+		BN_DIGIT(c, i) = 0;
 
-	bn_mont_mul_add(c, a ? a->d[0] : 1, b, nprime, N);
+	bn_mont_mul_add(c, a ? BN_DIGIT(a, 0) : 1, b, nprime, N);
 	for (i = 1; i < N->dmax; i++)
-		bn_mont_mul_add(c, a ? a->d[i] : 0, b, nprime, N);
+		bn_mont_mul_add(c, a ? BN_DIGIT(a, i) : 0, b, nprime, N);
 }
 
 /* Mongomery R * R % N, R = 1 << (1 + log2N). */
@@ -206,11 +205,11 @@ void bn_mont_modexp(struct BIGNUM *output, const struct BIGNUM *input,
 	bn_init(&acc, acc_buf, bn_size(N));
 	bn_init(&aR, aR_buf, bn_size(N));
 
-	nprime = bn_compute_nprime(N->d[0]);
+	nprime = bn_compute_nprime(BN_DIGIT(N, 0));
 	bn_compute_RR(&RR, N);
 	bn_mont_mul(&acc, NULL, &RR, nprime, N);      /* R = 1 * RR / R % N */
 	bn_mont_mul(&aR, input, &RR, nprime, N);      /* aR = a * RR / R % N */
-	output->d[0] = 1;
+	BN_DIGIT(output, 0) = 1;
 
 	/* TODO(ngm): burn stack space and use windowing. */
 	for (i = exp->dmax * BN_BITS2 - 1; i >= 0; i--) {
@@ -232,7 +231,7 @@ void bn_mont_modexp(struct BIGNUM *output, const struct BIGNUM *input,
 
 	bn_mont_mul(output, NULL, &acc, nprime, N);     /* Convert out. */
 	/* Copy to output buffer if necessary. */
-	if (acc.d != acc_buf) {
+	if (acc.d != (struct access_helper *) acc_buf) {
 		memcpy(acc.d, acc_buf, bn_size(output));
 		*output = acc;
 	}
diff --git a/chip/g/dcrypto/internal.h b/chip/g/dcrypto/internal.h
index 61db833a53..36aa35f6bf 100644
--- a/chip/g/dcrypto/internal.h
+++ b/chip/g/dcrypto/internal.h
@@ -89,10 +89,12 @@ void dcrypto_sha_wait(enum sha_mode mode, uint32_t *digest);
 #define BN_BYTES        4
 
 struct BIGNUM {
-	uint32_t dmax;            /* Size of d, in 32-bit words. */
-	uint32_t *d;              /* Word array, little endian format ... */
+	uint32_t dmax;              /* Size of d, in 32-bit words. */
+	struct access_helper *d;  /* Word array, little endian format ... */
 };
 
+#define BN_DIGIT(b, i) ((b)->d[(i)].udata)
+
 void bn_init(struct BIGNUM *bn, void *buf, size_t len);
 #define bn_size(b) ((b)->dmax * BN_BYTES)
 int bn_check_topbit(const struct BIGNUM *N);
diff --git a/chip/g/dcrypto/rsa.c b/chip/g/dcrypto/rsa.c
index d9774a2101..b6128923ef 100644
--- a/chip/g/dcrypto/rsa.c
+++ b/chip/g/dcrypto/rsa.c
@@ -339,7 +339,7 @@ int DCRYPTO_rsa_encrypt(struct RSA *rsa, uint8_t *out, uint32_t *out_len,
 	bn_init(&padded, padded_buf, bn_size(&rsa->N));
 	bn_init(&encrypted, out, bn_size(&rsa->N));
 	bn_init(&e, e_buf, sizeof(e_buf));
-	*e.d = rsa->e;
+	BN_DIGIT(&e, 0) = rsa->e;
 
 	switch (padding) {
 	case PADDING_MODE_OAEP:
@@ -479,7 +479,7 @@ int DCRYPTO_rsa_verify(struct RSA *rsa, const uint8_t *digest,
 	memcpy(signature_buf, sig, bn_size(&rsa->N));
 	bn_init(&padded, padded_buf, bn_size(&rsa->N));
 	bn_init(&e, e_buf, sizeof(e_buf));
-	*e.d = rsa->e;
+	BN_DIGIT(&e, 0) = rsa->e;
 
 	/* Reverse from big-endian to little-endian notation. */
 	reverse((uint8_t *) signature.d, signature.dmax * BN_BYTES);