CR50: add support for RSA PKCS1-PSS padding

Add support for PSS padding as per RFC 3447.

BRANCH=none
BUG=chrome-os-partner:43025,chrome-os-partner:47524
TEST=tests under tpm2 pass

Change-Id: I14c58394f742daa5de4ec2fbeb7e7f14e54c9fcc
Signed-off-by: nagendra modadugu <ngm@google.com>
Reviewed-on: https://chromium-review.googlesource.com/328778
Commit-Ready: Nagendra Modadugu <ngm@google.com>
Tested-by: Nagendra Modadugu <ngm@google.com>
Reviewed-by: Nagendra Modadugu <ngm@google.com>

4 files changed, 124 insertions, 6 deletions

diff --git a/board/cr50/tpm2/rsa.c b/board/cr50/tpm2/rsa.c
index b31a5012fb..526dc25c95 100644
--- a/board/cr50/tpm2/rsa.c
+++ b/board/cr50/tpm2/rsa.c
@@ -43,15 +43,18 @@ static int check_sign_params(TPM_ALG_ID padding_alg, TPM_ALG_ID hash_alg,
 			enum padding_mode *padding,
 			enum hashing_mode *hashing)
 {
-	/* TODO: add support for PSS. */
-	if (padding_alg == TPM_ALG_RSASSA) {
+	if (padding_alg == TPM_ALG_RSASSA ||
+		padding_alg == TPM_ALG_RSAPSS) {
 		if (hash_alg == TPM_ALG_SHA1)
 			*hashing = HASH_SHA1;
 		else if (hash_alg == TPM_ALG_SHA256)
 			*hashing = HASH_SHA256;
 		else
 			return 0;
-		*padding = PADDING_MODE_PKCS1;
+		if (padding_alg == TPM_ALG_RSASSA)
+			*padding = PADDING_MODE_PKCS1;
+		else
+			*padding = PADDING_MODE_PSS;
 	} else {
 		return 0;
 	}
diff --git a/chip/g/dcrypto/dcrypto.h b/chip/g/dcrypto/dcrypto.h
index c0422208ae..0856ec76c6 100644
--- a/chip/g/dcrypto/dcrypto.h
+++ b/chip/g/dcrypto/dcrypto.h
@@ -93,7 +93,8 @@ struct RSA {
 
 enum padding_mode {
 	PADDING_MODE_PKCS1 = 0,
-	PADDING_MODE_OAEP  = 1
+	PADDING_MODE_OAEP  = 1,
+	PADDING_MODE_PSS = 2
 };
 
 /* Calculate r = m ^ e mod N */
diff --git a/chip/g/dcrypto/rsa.c b/chip/g/dcrypto/rsa.c
index 5107773a30..02dbbf01f4 100644
--- a/chip/g/dcrypto/rsa.c
+++ b/chip/g/dcrypto/rsa.c
@@ -7,6 +7,7 @@
 #include "internal.h"
 
 #include "trng.h"
+#include "util.h"
 
 #include <assert.h>
 
@@ -297,6 +298,107 @@ static int check_pkcs1_type1_pad(const uint8_t *msg, uint32_t msg_len,
 	return memcmp(msg, &padded[i], hash_size) == 0;
 }
 
+/* sign */
+static int pkcs1_pss_pad(uint8_t *padded, uint32_t padded_len,
+			const uint8_t *in, uint32_t in_len,
+			enum hashing_mode hashing)
+{
+	const uint32_t hash_size = (hashing == HASH_SHA1) ? SHA1_DIGEST_BYTES
+		: SHA256_DIGEST_BYTES;
+	const uint32_t salt_len = MIN(padded_len - hash_size - 2, hash_size);
+	uint32_t db_len;
+	uint32_t ps_len;
+	struct HASH_CTX ctx;
+
+	if (in_len != hash_size)
+		return 0;
+	if (padded_len < hash_size + 2)
+		return 0;
+	db_len = padded_len - hash_size - 1;
+
+	if (hashing == HASH_SHA1)
+		DCRYPTO_SHA1_init(&ctx, 0);
+	else
+		DCRYPTO_SHA256_init(&ctx, 0);
+
+	/* Pilfer bits of output for temporary use. */
+	memset(padded, 0, 8);
+	DCRYPTO_HASH_update(&ctx, padded, 8);
+	DCRYPTO_HASH_update(&ctx, in, in_len);
+	/* Pilfer bits of output for temporary use. */
+	rand_bytes(padded, salt_len);
+	DCRYPTO_HASH_update(&ctx, padded, salt_len);
+
+	/* Output hash. */
+	memcpy(padded + db_len, DCRYPTO_HASH_final(&ctx), hash_size);
+
+	/* Prepare DB. */
+	ps_len = db_len - salt_len - 1;
+	memmove(padded + ps_len + 1, padded, salt_len);
+	memset(padded, 0, ps_len);
+	padded[ps_len] = 0x01;
+	MGF1_xor(padded, db_len, padded + db_len, hash_size, hashing);
+
+	/* Clear most significant bit. */
+	padded[0] &= 0x7F;
+	/* Set trailing byte. */
+	padded[padded_len - 1] = 0xBC;
+	return 1;
+}
+
+/* verify */
+static int check_pkcs1_pss_pad(const uint8_t *in, uint32_t in_len,
+			uint8_t *padded, uint32_t padded_len,
+			enum hashing_mode hashing)
+{
+	const uint32_t hash_size = (hashing == HASH_SHA1) ? SHA1_DIGEST_BYTES
+		: SHA256_DIGEST_BYTES;
+	const uint8_t zeros[8] = {0, 0, 0, 0, 0, 0, 0, 0};
+	uint32_t db_len;
+	uint32_t max_ps_len;
+	uint32_t salt_len;
+	struct HASH_CTX ctx;
+	int bad = 0;
+	int i;
+
+	if (in_len != hash_size)
+		return 0;
+	if (padded_len < hash_size + 2)
+		return 0;
+	db_len = padded_len - hash_size - 1;
+
+	/* Top bit should be zero. */
+	bad |= padded[0] & 0x80;
+	/* Check trailing byte. */
+	bad |= padded[padded_len - 1] ^ 0xBC;
+
+	/* Recover DB. */
+	MGF1_xor(padded, db_len, padded + db_len, hash_size, hashing);
+	/* Clear top bit. */
+	padded[0] &= 0x7F;
+	/* Verify padding2. */
+	max_ps_len = db_len - 1;
+	for (i = 0; i < max_ps_len; i++) {
+		if (padded[i] == 0x01)
+			break;
+		else
+			bad |= padded[i];
+	}
+	bad |= (padded[i] ^ 0x01);
+	/* Continue with zero-length salt if 0x01 was not found. */
+	salt_len = max_ps_len - i;
+
+	if (hashing == HASH_SHA1)
+		DCRYPTO_SHA1_init(&ctx, 0);
+	else
+		DCRYPTO_SHA256_init(&ctx, 0);
+	DCRYPTO_HASH_update(&ctx, zeros, sizeof(zeros));
+	DCRYPTO_HASH_update(&ctx, in, in_len);
+	DCRYPTO_HASH_update(&ctx, padded + db_len - salt_len, salt_len);
+	bad |= memcmp(padded + db_len, DCRYPTO_HASH_final(&ctx), hash_size);
+	return !bad;
+}
+
 static int check_modulus_params(const struct BIGNUM *N, uint32_t *out_len)
 {
 	if (bn_size(N) > RSA_MAX_BYTES)
@@ -421,13 +523,17 @@ int DCRYPTO_rsa_sign(struct RSA *rsa, uint8_t *out, uint32_t *out_len,
 	bn_init(&padded, padded_buf, bn_size(&rsa->N));
 	bn_init(&signature, out, bn_size(&rsa->N));
 
-	/* TODO(ngm): add support for PSS. */
 	switch (padding) {
 	case PADDING_MODE_PKCS1:
 		if (!pkcs1_type1_pad((uint8_t *) padded.d, bn_size(&padded),
 					(const uint8_t *) in, in_len, hashing))
 			return 0;
 		break;
+	case PADDING_MODE_PSS:
+		if (!pkcs1_pss_pad((uint8_t *) padded.d, bn_size(&padded),
+					(const uint8_t *) in, in_len, hashing))
+			return 0;
+		break;
 	default:
 		return 0;
 	}
@@ -481,6 +587,12 @@ int DCRYPTO_rsa_verify(struct RSA *rsa, const uint8_t *digest,
 				bn_size(&padded), hashing))
 			ret = 0;
 		break;
+	case PADDING_MODE_PSS:
+		if (!check_pkcs1_pss_pad(
+				digest, digest_len, (uint8_t *) padded.d,
+				bn_size(&padded), hashing))
+			return 0;
+		break;
 	default:
 		/* Unsupported padding mode. */
 		ret = 0;
diff --git a/test/tpm_test/rsa_test.py b/test/tpm_test/rsa_test.py
index 0783f957fd..37ffbd2677 100644
--- a/test/tpm_test/rsa_test.py
+++ b/test/tpm_test/rsa_test.py
@@ -25,6 +25,7 @@ _RSA_OPCODES = {
 _RSA_PADDING = {
   'PKCS1-SSA': 0x14,
   'PKCS1-ES': 0x15,
+  'PKCS1-PSS': 0x16,
   'OAEP': 0x17
 }
 
@@ -113,9 +114,10 @@ _ENCRYPT_INPUTS = (
 
 
 _SIGN_INPUTS = (
-  # TODO(ngm): add support for PSS.
   ('PKCS1-SSA', 'SHA1', 768),
   ('PKCS1-SSA', 'SHA256', 768),
+  ('PKCS1-PSS', 'SHA1', 768),
+  ('PKCS1-PSS', 'SHA256', 768),
 )