Add back support for RSA_X931_PADDING

This makes the custom stalt stack work again.

Tested by robert as part of a larger diff
ok jsing

3 files changed, 127 insertions, 65 deletions

diff --git a/src/lib/libcrypto/rsa/rsa_eay.c b/src/lib/libcrypto/rsa/rsa_eay.c
index e65319bda1..6db563f2a4 100644
--- a/src/lib/libcrypto/rsa/rsa_eay.c
+++ b/src/lib/libcrypto/rsa/rsa_eay.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: rsa_eay.c,v 1.59 2023/04/15 18:48:52 tb Exp $ */
+/* $OpenBSD: rsa_eay.c,v 1.60 2023/05/05 12:21:44 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -382,11 +382,14 @@ RSA_eay_private_encrypt(int flen, const unsigned char *from, unsigned char *to,
         case RSA_PKCS1_PADDING:
                 i = RSA_padding_add_PKCS1_type_1(buf, num, from, flen);
                 break;
+        case RSA_X931_PADDING:
+                i = RSA_padding_add_X931(buf, num, from, flen);
+                break;
         case RSA_NO_PADDING:
                 i = RSA_padding_add_none(buf, num, from, flen);
                 break;
         default:
-                RSAerror(RSA_R_ILLEGAL_OR_UNSUPPORTED_PADDING_MODE);
+                RSAerror(RSA_R_UNKNOWN_PADDING_TYPE);
                 goto err;
         }
         if (i <= 0)
@@ -446,11 +449,14 @@ RSA_eay_private_encrypt(int flen, const unsigned char *from, unsigned char *to,
                         goto err;
 
         if (padding == RSA_X931_PADDING) {
-                RSAerror(RSA_R_ILLEGAL_OR_UNSUPPORTED_PADDING_MODE);
-                goto err;
-        }
-
-        res = ret;
+                if (!BN_sub(f, rsa->n, ret))
+                        goto err;
+                if (BN_cmp(ret, f) > 0)
+                        res = f;
+                else
+                        res = ret;
+        } else
+                res = ret;
 
         /* put in leading 0 bytes if the number is less than the
          * length of the modulus */
@@ -661,10 +667,9 @@ RSA_eay_public_decrypt(int flen, const unsigned char *from, unsigned char *to,
             rsa->_method_mod_n))
                 goto err;
 
-        if (padding == RSA_X931_PADDING) {
-                RSAerror(RSA_R_ILLEGAL_OR_UNSUPPORTED_PADDING_MODE);
-                goto err;
-        }
+        if (padding == RSA_X931_PADDING && (ret->d[0] & 0xf) != 12)
+                if (!BN_sub(ret, rsa->n, ret))
+                        goto err;
 
         p = buf;
         i = BN_bn2bin(ret, p);
@@ -673,6 +678,9 @@ RSA_eay_public_decrypt(int flen, const unsigned char *from, unsigned char *to,
         case RSA_PKCS1_PADDING:
                 r = RSA_padding_check_PKCS1_type_1(to, num, buf, i, num);
                 break;
+        case RSA_X931_PADDING:
+                r = RSA_padding_check_X931(to, num, buf, i, num);
+                break;
         case RSA_NO_PADDING:
                 r = RSA_padding_check_none(to, num, buf, i, num);
                 break;
diff --git a/src/lib/libcrypto/rsa/rsa_local.h b/src/lib/libcrypto/rsa/rsa_local.h
index b438ab4eec..4bc2cee8cd 100644
--- a/src/lib/libcrypto/rsa/rsa_local.h
+++ b/src/lib/libcrypto/rsa/rsa_local.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: rsa_local.h,v 1.1 2022/11/26 16:08:54 tb Exp $ */
+/* $OpenBSD: rsa_local.h,v 1.2 2023/05/05 12:21:44 tb Exp $ */
 
 __BEGIN_HIDDEN_DECLS
 
@@ -91,4 +91,10 @@ extern int int_rsa_verify(int dtype, const unsigned char *m,
     unsigned int m_len, unsigned char *rm, size_t *prm_len,
     const unsigned char *sigbuf, size_t siglen, RSA *rsa);
 
+int RSA_padding_add_X931(unsigned char *to, int tlen,
+    const unsigned char *f, int fl);
+int RSA_padding_check_X931(unsigned char *to, int tlen,
+    const unsigned char *f, int fl, int rsa_len);
+int RSA_X931_hash_id(int nid);
+
 __END_HIDDEN_DECLS
diff --git a/src/lib/libcrypto/rsa/rsa_pmeth.c b/src/lib/libcrypto/rsa/rsa_pmeth.c
index 8e06365566..429524d73d 100644
--- a/src/lib/libcrypto/rsa/rsa_pmeth.c
+++ b/src/lib/libcrypto/rsa/rsa_pmeth.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: rsa_pmeth.c,v 1.37 2023/04/25 15:48:48 tb Exp $ */
+/* $OpenBSD: rsa_pmeth.c,v 1.38 2023/05/05 12:21:44 tb Exp $ */
 /* Written by Dr Stephen N Henson (steve@openssl.org) for the OpenSSL
  * project 2006.
  */
@@ -187,7 +187,7 @@ static int
 pkey_rsa_sign(EVP_PKEY_CTX *ctx, unsigned char *sig, size_t *siglen,
     const unsigned char *tbs, size_t tbslen)
 {
-        int ret = -1;
+        int ret;
         RSA_PKEY_CTX *rctx = ctx->data;
         RSA *rsa = ctx->pkey->pkey.rsa;
 
@@ -197,11 +197,21 @@ pkey_rsa_sign(EVP_PKEY_CTX *ctx, unsigned char *sig, size_t *siglen,
                         return -1;
                 }
 
-                if (rctx->pad_mode != RSA_PKCS1_PADDING &&
-                    rctx->pad_mode != RSA_PKCS1_PSS_PADDING)
-                        return -1;
-
-                if (rctx->pad_mode == RSA_PKCS1_PADDING) {
+                if (rctx->pad_mode == RSA_X931_PADDING) {
+                        if ((size_t)EVP_PKEY_size(ctx->pkey) < tbslen + 1) {
+                                RSAerror(RSA_R_KEY_SIZE_TOO_SMALL);
+                                return -1;
+                        }
+                        if (!setup_tbuf(rctx, ctx)) {
+                                RSAerror(ERR_R_MALLOC_FAILURE);
+                                return -1;
+                        }
+                        memcpy(rctx->tbuf, tbs, tbslen);
+                        rctx->tbuf[tbslen] =
+                            RSA_X931_hash_id(EVP_MD_type(rctx->md));
+                        ret = RSA_private_encrypt(tbslen + 1, rctx->tbuf, sig,
+                            rsa, RSA_X931_PADDING);
+                } else if (rctx->pad_mode == RSA_PKCS1_PADDING) {
                         unsigned int sltmp;
 
                         ret = RSA_sign(EVP_MD_type(rctx->md), tbs, tbslen, sig,
@@ -217,6 +227,8 @@ pkey_rsa_sign(EVP_PKEY_CTX *ctx, unsigned char *sig, size_t *siglen,
                                 return -1;
                         ret = RSA_private_encrypt(RSA_size(rsa), rctx->tbuf,
                             sig, rsa, RSA_NO_PADDING);
+                } else {
+                        return -1;
                 }
         } else {
                 ret = RSA_private_encrypt(tbslen, tbs, sig, ctx->pkey->pkey.rsa,
@@ -236,16 +248,36 @@ pkey_rsa_verifyrecover(EVP_PKEY_CTX *ctx, unsigned char *rout, size_t *routlen,
         RSA_PKEY_CTX *rctx = ctx->data;
 
         if (rctx->md) {
-                size_t sltmp;
+                if (rctx->pad_mode == RSA_X931_PADDING) {
+                        if (!setup_tbuf(rctx, ctx))
+                                return -1;
+                        ret = RSA_public_decrypt(siglen, sig, rctx->tbuf,
+                            ctx->pkey->pkey.rsa, RSA_X931_PADDING);
+                        if (ret < 1)
+                                return 0;
+                        ret--;
+                        if (rctx->tbuf[ret] !=
+                            RSA_X931_hash_id(EVP_MD_type(rctx->md))) {
+                                RSAerror(RSA_R_ALGORITHM_MISMATCH);
+                                return 0;
+                        }
+                        if (ret != EVP_MD_size(rctx->md)) {
+                                RSAerror(RSA_R_INVALID_DIGEST_LENGTH);
+                                return 0;
+                        }
+                        if (rout)
+                                memcpy(rout, rctx->tbuf, ret);
+                } else if (rctx->pad_mode == RSA_PKCS1_PADDING) {
+                        size_t sltmp;
 
-                if (rctx->pad_mode != RSA_PKCS1_PADDING)
+                        ret = int_rsa_verify(EVP_MD_type(rctx->md), NULL, 0,
+                            rout, &sltmp, sig, siglen, ctx->pkey->pkey.rsa);
+                        if (ret <= 0)
+                                return 0;
+                        ret = sltmp;
+                } else {
                         return -1;
-
-                ret = int_rsa_verify(EVP_MD_type(rctx->md), NULL, 0,
-                    rout, &sltmp, sig, siglen, ctx->pkey->pkey.rsa);
-                if (ret <= 0)
-                        return 0;
-                ret = sltmp;
+                }
         } else {
                 ret = RSA_public_decrypt(siglen, sig, rout, ctx->pkey->pkey.rsa,
                     rctx->pad_mode);
@@ -263,7 +295,6 @@ pkey_rsa_verify(EVP_PKEY_CTX *ctx, const unsigned char *sig, size_t siglen,
         RSA_PKEY_CTX *rctx = ctx->data;
         RSA *rsa = ctx->pkey->pkey.rsa;
         size_t rslen;
-        int ret;
 
         if (rctx->md) {
                 if (rctx->pad_mode == RSA_PKCS1_PADDING)
@@ -273,22 +304,30 @@ pkey_rsa_verify(EVP_PKEY_CTX *ctx, const unsigned char *sig, size_t siglen,
                         RSAerror(RSA_R_INVALID_DIGEST_LENGTH);
                         return -1;
                 }
+                if (rctx->pad_mode == RSA_X931_PADDING) {
+                        if (pkey_rsa_verifyrecover(ctx, NULL, &rslen, sig,
+                            siglen) <= 0)
+                                return 0;
+                } else if (rctx->pad_mode == RSA_PKCS1_PSS_PADDING) {
+                        int ret;
 
-                if (rctx->pad_mode != RSA_PKCS1_PSS_PADDING)
-                        return -1;
-
-                if (!setup_tbuf(rctx, ctx))
+                        if (!setup_tbuf(rctx, ctx))
+                                return -1;
+                        ret = RSA_public_decrypt(siglen, sig, rctx->tbuf,
+                            rsa, RSA_NO_PADDING);
+                        if (ret <= 0)
+                                return 0;
+                        ret = RSA_verify_PKCS1_PSS_mgf1(rsa, tbs, rctx->md,
+                            rctx->mgf1md, rctx->tbuf, rctx->saltlen);
+                        if (ret <= 0)
+                                return 0;
+                        return 1;
+                } else {
                         return -1;
-                ret = RSA_public_decrypt(siglen, sig, rctx->tbuf,
-                    rsa, RSA_NO_PADDING);
-                if (ret <= 0)
-                        return 0;
-                ret = RSA_verify_PKCS1_PSS_mgf1(rsa, tbs, rctx->md,
-                    rctx->mgf1md, rctx->tbuf, rctx->saltlen);
-                if (ret <= 0)
-                        return 0;
-                return 1;
+                }
         } else {
+                int ret;
+
                 if (!setup_tbuf(rctx, ctx))
                         return -1;
 
@@ -365,34 +404,41 @@ check_padding_md(const EVP_MD *md, int padding)
         if (md == NULL)
                 return 1;
 
-        if (padding == RSA_NO_PADDING || padding == RSA_X931_PADDING) {
-                RSAerror(RSA_R_ILLEGAL_OR_UNSUPPORTED_PADDING_MODE);
+        if (padding == RSA_NO_PADDING) {
+                RSAerror(RSA_R_INVALID_PADDING_MODE);
                 return 0;
         }
 
-        /* List of all supported RSA digests. */
-        /* RFC 8017 and NIST CSOR. */
-        switch(EVP_MD_type(md)) {
-        case NID_sha1:
-        case NID_sha224:
-        case NID_sha256:
-        case NID_sha384:
-        case NID_sha512:
-        case NID_sha512_224:
-        case NID_sha512_256:
-        case NID_sha3_224:
-        case NID_sha3_256:
-        case NID_sha3_384:
-        case NID_sha3_512:
-        case NID_md5:
-        case NID_md5_sha1:
-        case NID_md4:
-        case NID_ripemd160:
-                return 1;
+        if (padding == RSA_X931_PADDING) {
+                if (RSA_X931_hash_id(EVP_MD_type(md)) == -1) {
+                        RSAerror(RSA_R_INVALID_X931_DIGEST);
+                        return 0;
+                }
+        } else {
+                /* List of all supported RSA digests. */
+                /* RFC 8017 and NIST CSOR. */
+                switch(EVP_MD_type(md)) {
+                case NID_sha1:
+                case NID_sha224:
+                case NID_sha256:
+                case NID_sha384:
+                case NID_sha512:
+                case NID_sha512_224:
+                case NID_sha512_256:
+                case NID_sha3_224:
+                case NID_sha3_256:
+                case NID_sha3_384:
+                case NID_sha3_512:
+                case NID_md5:
+                case NID_md5_sha1:
+                case NID_md4:
+                case NID_ripemd160:
+                        return 1;
 
-        default:
-                RSAerror(RSA_R_INVALID_DIGEST);
-                return 0;
+                default:
+                        RSAerror(RSA_R_INVALID_DIGEST);
+                        return 0;
+                }
         }
 
         return 1;
@@ -598,6 +644,8 @@ pkey_rsa_ctrl_str(EVP_PKEY_CTX *ctx, const char *type, const char *value)
                         pm = RSA_PKCS1_OAEP_PADDING;
                 else if (!strcmp(value, "oaep"))
                         pm = RSA_PKCS1_OAEP_PADDING;
+                else if (!strcmp(value, "x931"))
+                        pm = RSA_X931_PADDING;
                 else if (!strcmp(value, "pss"))
                         pm = RSA_PKCS1_PSS_PADDING;
                 else {