/* * PDKIM - a RFC4871 (DKIM) implementation * * Copyright (C) 2016 Exim maintainers * * RSA signing/verification interface XXX rename interfaces to cover all signature methods. the method (algo) needs to be extracted from the supplied private-key and not only stashed as needed in the sign- or verify- context, but indicated to caller for protocol tag construction. */ #include "../exim.h" #ifndef DISABLE_DKIM /* entire file */ #ifndef SUPPORT_TLS # error Need SUPPORT_TLS for DKIM #endif #include "crypt_ver.h" #include "signing.h" /******************************************************************************/ #ifdef RSA_GNUTLS void exim_dkim_init(void) { } /* accumulate data (gnutls-only). String to be appended must be nul-terminated. */ blob * exim_dkim_data_append(blob * b, int * alloc, uschar * s) { int len = b->len; b->data = string_append(b->data, alloc, &len, 1, s); b->len = len; return b; } /* import private key from PEM string in memory. Return: NULL for success, or an error string */ const uschar * exim_dkim_signing_init(uschar * privkey_pem, es_ctx * sign_ctx) { gnutls_datum_t k; int rc; k.data = privkey_pem; k.size = strlen(privkey_pem); if ( (rc = gnutls_x509_privkey_init(&sign_ctx->rsa)) != GNUTLS_E_SUCCESS || (rc = gnutls_x509_privkey_import(sign_ctx->rsa, &k, GNUTLS_X509_FMT_PEM)) != GNUTLS_E_SUCCESS ) return gnutls_strerror(rc); return NULL; } /* allocate mem for signature (when signing) */ /* sign data (gnutls_only) OR sign hash. Return: NULL for success, or an error string */ const uschar * exim_dkim_sign(es_ctx * sign_ctx, BOOL is_sha1, blob * data, blob * sig) { gnutls_datum_t k; size_t sigsize = 0; int rc; const uschar * ret = NULL; /* Allocate mem for signature */ k.data = data->data; k.size = data->len; (void) gnutls_x509_privkey_sign_data(sign_ctx->rsa, is_sha1 ? GNUTLS_DIG_SHA1 : GNUTLS_DIG_SHA256, 0, &k, NULL, &sigsize); sig->data = store_get(sigsize); sig->len = sigsize; /* Do signing */ /*XXX will need extension for hash type; looks ok for non-RSA algos so long as the privkey_import stage got them. */ if ((rc = gnutls_x509_privkey_sign_data(sign_ctx->rsa, is_sha1 ? GNUTLS_DIG_SHA1 : GNUTLS_DIG_SHA256, 0, &k, sig->data, &sigsize)) != GNUTLS_E_SUCCESS ) ret = gnutls_strerror(rc); gnutls_x509_privkey_deinit(sign_ctx->rsa); return ret; } /* import public key (from DER in memory) Return: NULL for success, or an error string */ const uschar * exim_dkim_verify_init(blob * pubkey_der, ev_ctx * verify_ctx) { gnutls_datum_t k; int rc; const uschar * ret = NULL; gnutls_pubkey_init(&verify_ctx->rsa); k.data = pubkey_der->data; k.size = pubkey_der->len; if ((rc = gnutls_pubkey_import(verify_ctx->rsa, &k, GNUTLS_X509_FMT_DER)) != GNUTLS_E_SUCCESS) ret = gnutls_strerror(rc); return ret; } /* verify signature (of hash) (given pubkey & alleged sig) Return: NULL for success, or an error string */ const uschar * exim_dkim_verify(ev_ctx * verify_ctx, BOOL is_sha1, blob * data_hash, blob * sig) { gnutls_datum_t k, s; int rc; const uschar * ret = NULL; k.data = data_hash->data; k.size = data_hash->len; s.data = sig->data; s.size = sig->len; if ((rc = gnutls_pubkey_verify_hash2(verify_ctx->rsa, /*XXX needs extension for SHA512 */ is_sha1 ? GNUTLS_SIGN_RSA_SHA1 : GNUTLS_SIGN_RSA_SHA256, 0, &k, &s)) < 0) ret = gnutls_strerror(rc); gnutls_pubkey_deinit(verify_ctx->rsa); return ret; } #elif defined(RSA_GCRYPT) /******************************************************************************/ /* Internal service routine: Read and move past an asn.1 header, checking class & tag, optionally returning the data-length */ static int as_tag(blob * der, uschar req_cls, long req_tag, long * alen) { int rc; uschar tag_class; int taglen; long tag, len; /* debug_printf_indent("as_tag: %02x %02x %02x %02x\n", der->data[0], der->data[1], der->data[2], der->data[3]); */ if ((rc = asn1_get_tag_der(der->data++, der->len--, &tag_class, &taglen, &tag)) != ASN1_SUCCESS) return rc; if (tag_class != req_cls || tag != req_tag) return ASN1_ELEMENT_NOT_FOUND; if ((len = asn1_get_length_der(der->data, der->len, &taglen)) < 0) return ASN1_DER_ERROR; if (alen) *alen = len; /* debug_printf_indent("as_tag: tlen %d dlen %d\n", taglen, (int)len); */ der->data += taglen; der->len -= taglen; return rc; } /* Internal service routine: Read and move over an asn.1 integer, setting an MPI to the value */ static uschar * as_mpi(blob * der, gcry_mpi_t * mpi) { long alen; int rc; gcry_error_t gerr; /* integer; move past the header */ if ((rc = as_tag(der, 0, ASN1_TAG_INTEGER, &alen)) != ASN1_SUCCESS) return US asn1_strerror(rc); /* read to an MPI */ if ((gerr = gcry_mpi_scan(mpi, GCRYMPI_FMT_STD, der->data, alen, NULL))) return US gcry_strerror(gerr); /* move over the data */ der->data += alen; der->len -= alen; return NULL; } void exim_dkim_init(void) { /* Version check should be the very first call because it makes sure that important subsystems are initialized. */ if (!gcry_check_version (GCRYPT_VERSION)) { fputs ("libgcrypt version mismatch\n", stderr); exit (2); } /* We don't want to see any warnings, e.g. because we have not yet parsed program options which might be used to suppress such warnings. */ gcry_control (GCRYCTL_SUSPEND_SECMEM_WARN); /* ... If required, other initialization goes here. Note that the process might still be running with increased privileges and that the secure memory has not been initialized. */ /* Allocate a pool of 16k secure memory. This make the secure memory available and also drops privileges where needed. */ gcry_control (GCRYCTL_INIT_SECMEM, 16384, 0); /* It is now okay to let Libgcrypt complain when there was/is a problem with the secure memory. */ gcry_control (GCRYCTL_RESUME_SECMEM_WARN); /* ... If required, other initialization goes here. */ /* Tell Libgcrypt that initialization has completed. */ gcry_control (GCRYCTL_INITIALIZATION_FINISHED, 0); return; } /* Accumulate data (gnutls-only). String to be appended must be nul-terminated. */ blob * exim_dkim_data_append(blob * b, int * alloc, uschar * s) { return b; /*dummy*/ } /* import private key from PEM string in memory. Return: NULL for success, or an error string */ const uschar * exim_dkim_signing_init(uschar * privkey_pem, es_ctx * sign_ctx) { uschar * s1, * s2; blob der; long alen; int rc; /*XXX will need extension to _spot_ as well as handle a non-RSA key? I think... */ /* * RSAPrivateKey ::= SEQUENCE * version Version, * modulus INTEGER, -- n * publicExponent INTEGER, -- e * privateExponent INTEGER, -- d * prime1 INTEGER, -- p * prime2 INTEGER, -- q * exponent1 INTEGER, -- d mod (p-1) * exponent2 INTEGER, -- d mod (q-1) * coefficient INTEGER, -- (inverse of q) mod p * otherPrimeInfos OtherPrimeInfos OPTIONAL */ if ( !(s1 = Ustrstr(CS privkey_pem, "-----BEGIN RSA PRIVATE KEY-----")) || !(s2 = Ustrstr(CS (s1+=31), "-----END RSA PRIVATE KEY-----" )) ) return US"Bad PEM wrapper"; *s2 = '\0'; if ((der.len = b64decode(s1, &der.data)) < 0) return US"Bad PEM-DER b64 decode"; /* untangle asn.1 */ /* sequence; just move past the header */ if ((rc = as_tag(&der, ASN1_CLASS_STRUCTURED, ASN1_TAG_SEQUENCE, NULL)) != ASN1_SUCCESS) goto asn_err; /* integer version; move past the header, check is zero */ if ((rc = as_tag(&der, 0, ASN1_TAG_INTEGER, &alen)) != ASN1_SUCCESS) goto asn_err; if (alen != 1 || *der.data != 0) return US"Bad version number"; der.data++; der.len--; if ( (s1 = as_mpi(&der, &sign_ctx->n)) || (s1 = as_mpi(&der, &sign_ctx->e)) || (s1 = as_mpi(&der, &sign_ctx->d)) || (s1 = as_mpi(&der, &sign_ctx->p)) || (s1 = as_mpi(&der, &sign_ctx->q)) || (s1 = as_mpi(&der, &sign_ctx->dp)) || (s1 = as_mpi(&der, &sign_ctx->dq)) || (s1 = as_mpi(&der, &sign_ctx->qp)) ) return s1; DEBUG(D_acl) debug_printf_indent("rsa_signing_init:\n"); { uschar * s; gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->n); debug_printf_indent(" N : %s\n", s); gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->e); debug_printf_indent(" E : %s\n", s); gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->d); debug_printf_indent(" D : %s\n", s); gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->p); debug_printf_indent(" P : %s\n", s); gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->q); debug_printf_indent(" Q : %s\n", s); gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->dp); debug_printf_indent(" DP: %s\n", s); gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->dq); debug_printf_indent(" DQ: %s\n", s); gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->qp); debug_printf_indent(" QP: %s\n", s); } return NULL; asn_err: return US asn1_strerror(rc); } /* allocate mem for signature (when signing) */ /* sign data (gnutls_only) OR sign hash. Return: NULL for success, or an error string */ const uschar * exim_dkim_sign(es_ctx * sign_ctx, BOOL is_sha1, blob * data, blob * sig) { gcry_sexp_t s_hash = NULL, s_key = NULL, s_sig = NULL; gcry_mpi_t m_sig; uschar * errstr; gcry_error_t gerr; /*XXX will need extension for hash types (though, possibly, should be re-specced to not rehash but take an already-hashed value? Actually current impl looks WRONG - it _is_ given a has so should not be re-hashing. Has this been tested? Will need extension for non-RSA sugning algos. */ #define SIGSPACE 128 sig->data = store_get(SIGSPACE); if (gcry_mpi_cmp (sign_ctx->p, sign_ctx->q) > 0) { gcry_mpi_swap (sign_ctx->p, sign_ctx->q); gcry_mpi_invm (sign_ctx->qp, sign_ctx->p, sign_ctx->q); } if ( (gerr = gcry_sexp_build (&s_key, NULL, "(private-key (rsa (n%m)(e%m)(d%m)(p%m)(q%m)(u%m)))", sign_ctx->n, sign_ctx->e, sign_ctx->d, sign_ctx->p, sign_ctx->q, sign_ctx->qp)) || (gerr = gcry_sexp_build (&s_hash, NULL, is_sha1 ? "(data(flags pkcs1)(hash sha1 %b))" : "(data(flags pkcs1)(hash sha256 %b))", (int) data->len, CS data->data)) || (gerr = gcry_pk_sign (&s_sig, s_hash, s_key)) ) return US gcry_strerror(gerr); /* gcry_sexp_dump(s_sig); */ if ( !(s_sig = gcry_sexp_find_token(s_sig, "s", 0)) ) return US"no sig result"; m_sig = gcry_sexp_nth_mpi(s_sig, 1, GCRYMPI_FMT_USG); DEBUG(D_acl) { uschar * s; gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, m_sig); debug_printf_indent(" SG: %s\n", s); } gerr = gcry_mpi_print(GCRYMPI_FMT_USG, sig->data, SIGSPACE, &sig->len, m_sig); if (gerr) { debug_printf_indent("signature conversion from MPI to buffer failed\n"); return US gcry_strerror(gerr); } #undef SIGSPACE return NULL; } /* import public key (from DER in memory) Return: NULL for success, or an error string */ const uschar * exim_dkim_verify_init(blob * pubkey_der, ev_ctx * verify_ctx) { /* in code sequence per b81207d2bfa92 rsa_parse_public_key() and asn1_get_mpi() */ uschar tag_class; int taglen; long alen; int rc; uschar * errstr; gcry_error_t gerr; uschar * stage = US"S1"; /* sequence sequence OBJECT:rsaEncryption NULL BIT STRING:RSAPublicKey sequence INTEGER:Public modulus INTEGER:Public exponent openssl rsa -in aux-fixed/dkim/dkim.private -pubout -outform DER | od -t x1 | head; openssl rsa -in aux-fixed/dkim/dkim.private -pubout | openssl asn1parse -dump; openssl rsa -in aux-fixed/dkim/dkim.private -pubout | openssl asn1parse -dump -offset 22; */ /* sequence; just move past the header */ if ((rc = as_tag(pubkey_der, ASN1_CLASS_STRUCTURED, ASN1_TAG_SEQUENCE, NULL)) != ASN1_SUCCESS) goto asn_err; /* sequence; skip the entire thing */ DEBUG(D_acl) stage = US"S2"; if ((rc = as_tag(pubkey_der, ASN1_CLASS_STRUCTURED, ASN1_TAG_SEQUENCE, &alen)) != ASN1_SUCCESS) goto asn_err; pubkey_der->data += alen; pubkey_der->len -= alen; /* bitstring: limit range to size of bitstring; move over header + content wrapper */ DEBUG(D_acl) stage = US"BS"; if ((rc = as_tag(pubkey_der, 0, ASN1_TAG_BIT_STRING, &alen)) != ASN1_SUCCESS) goto asn_err; pubkey_der->len = alen; pubkey_der->data++; pubkey_der->len--; /* sequence; just move past the header */ DEBUG(D_acl) stage = US"S3"; if ((rc = as_tag(pubkey_der, ASN1_CLASS_STRUCTURED, ASN1_TAG_SEQUENCE, NULL)) != ASN1_SUCCESS) goto asn_err; /* read two integers */ DEBUG(D_acl) stage = US"MPI"; if ( (errstr = as_mpi(pubkey_der, &verify_ctx->n)) || (errstr = as_mpi(pubkey_der, &verify_ctx->e)) ) return errstr; DEBUG(D_acl) debug_printf_indent("rsa_verify_init:\n"); { uschar * s; gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, verify_ctx->n); debug_printf_indent(" N : %s\n", s); gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, verify_ctx->e); debug_printf_indent(" E : %s\n", s); } return NULL; asn_err: DEBUG(D_acl) return string_sprintf("%s: %s", stage, asn1_strerror(rc)); return US asn1_strerror(rc); } /* verify signature (of hash) (given pubkey & alleged sig) Return: NULL for success, or an error string */ const uschar * exim_dkim_verify(ev_ctx * verify_ctx, BOOL is_sha1, blob * data_hash, blob * sig) { /* cf. libgnutls 2.8.5 _wrap_gcry_pk_verify() */ gcry_mpi_t m_sig; gcry_sexp_t s_sig = NULL, s_hash = NULL, s_pkey = NULL; gcry_error_t gerr; uschar * stage; if ( (stage = US"pkey sexp build", gerr = gcry_sexp_build (&s_pkey, NULL, "(public-key(rsa(n%m)(e%m)))", verify_ctx->n, verify_ctx->e)) || (stage = US"data sexp build", gerr = gcry_sexp_build (&s_hash, NULL, /*XXX needs extension for SHA512 */ is_sha1 ? "(data(flags pkcs1)(hash sha1 %b))" : "(data(flags pkcs1)(hash sha256 %b))", (int) data_hash->len, CS data_hash->data)) || (stage = US"sig mpi scan", gerr = gcry_mpi_scan(&m_sig, GCRYMPI_FMT_USG, sig->data, sig->len, NULL)) || (stage = US"sig sexp build", gerr = gcry_sexp_build (&s_sig, NULL, "(sig-val(rsa(s%m)))", m_sig)) || (stage = US"verify", gerr = gcry_pk_verify (s_sig, s_hash, s_pkey)) ) { DEBUG(D_acl) debug_printf_indent("verify: error in stage '%s'\n", stage); return US gcry_strerror(gerr); } if (s_sig) gcry_sexp_release (s_sig); if (s_hash) gcry_sexp_release (s_hash); if (s_pkey) gcry_sexp_release (s_pkey); gcry_mpi_release (m_sig); gcry_mpi_release (verify_ctx->n); gcry_mpi_release (verify_ctx->e); return NULL; } #elif defined(RSA_OPENSSL) /******************************************************************************/ void exim_dkim_init(void) { } /* accumulate data (gnutls-only) */ blob * exim_dkim_data_append(blob * b, int * alloc, uschar * s) { return b; /*dummy*/ } /* import private key from PEM string in memory. Return: NULL for success, or an error string */ const uschar * exim_dkim_signing_init(uschar * privkey_pem, es_ctx * sign_ctx) { uschar * p, * q; int len; /*XXX maybe use PEM_read_bio_PrivateKey() ??? The sign_ctx would need to have an EVP_PKEY* */ /* Convert PEM to DER */ if ( !(p = Ustrstr(privkey_pem, "-----BEGIN RSA PRIVATE KEY-----")) || !(q = Ustrstr(p+=31, "-----END RSA PRIVATE KEY-----")) ) return US"Bad PEM wrapping"; *q = '\0'; if ((len = b64decode(p, &p)) < 0) return US"b64decode failed"; if (!(sign_ctx->rsa = d2i_RSAPrivateKey(NULL, CUSS &p, len))) { char ssl_errstring[256]; ERR_load_crypto_strings(); /*XXX move to a startup routine */ ERR_error_string(ERR_get_error(), ssl_errstring); return string_copy(US ssl_errstring); } return NULL; } /* allocate mem for signature (when signing) */ /* sign data (gnutls_only) OR sign hash. Return: NULL for success, or an error string */ const uschar * exim_dkim_sign(es_ctx * sign_ctx, BOOL is_sha1, blob * data, blob * sig) { uint len; const uschar * ret = NULL; /*XXX will need extension for non-RSA signing algo. Maybe use https://www.openssl.org/docs/man1.0.2/crypto/EVP_PKEY_sign.html ??? */ /* Allocate mem for signature */ len = RSA_size(sign_ctx->rsa); sig->data = store_get(len); sig->len = len; /* Do signing */ if (RSA_sign(is_sha1 ? NID_sha1 : NID_sha256, CUS data->data, data->len, US sig->data, &len, sign_ctx->rsa) != 1) { char ssl_errstring[256]; ERR_load_crypto_strings(); /*XXX move to a startup routine */ ERR_error_string(ERR_get_error(), ssl_errstring); ret = string_copy(US ssl_errstring); } RSA_free(sign_ctx->rsa); return ret;; } /* import public key (from DER in memory) Return: NULL for success, or an error string */ const uschar * exim_dkim_verify_init(blob * pubkey_der, ev_ctx * verify_ctx) { const uschar * p = CUS pubkey_der->data; const uschar * ret = NULL; /*XXX d2i_X509_PUBKEY, X509_get_pubkey(), and an EVP_PKEY* in verify_ctx. */ if (!(verify_ctx->rsa = d2i_RSA_PUBKEY(NULL, &p, (long) pubkey_der->len))) { char ssl_errstring[256]; ERR_load_crypto_strings(); /*XXX move to a startup routine */ ERR_error_string(ERR_get_error(), ssl_errstring); ret = string_copy(CUS ssl_errstring); } return ret; } /* verify signature (of hash) (given pubkey & alleged sig) Return: NULL for success, or an error string */ const uschar * exim_dkim_verify(ev_ctx * verify_ctx, BOOL is_sha1, blob * data_hash, blob * sig) { const uschar * ret = NULL; /*XXX needs extension for SHA512, Possibly EVP_PKEY_verify() is all we need??? */ /* with EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) - see example code at https://www.openssl.org/docs/man1.0.2/crypto/EVP_PKEY_verify.html and maybe also EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) though unclear if that only sets a pad/type field byte value, or sets up for an actual hash operation... Same on the signing side. https://www.openssl.org/docs/manmaster/man3/EVP_PKEY_CTX_set_rsa_padding.html says it does what we want. */ if (RSA_verify(is_sha1 ? NID_sha1 : NID_sha256, CUS data_hash->data, data_hash->len, US sig->data, (uint) sig->len, verify_ctx->rsa) != 1) { char ssl_errstring[256]; ERR_load_crypto_strings(); /*XXX move to a startup routine */ ERR_error_string(ERR_get_error(), ssl_errstring); ret = string_copy(US ssl_errstring); } return ret; } #endif /******************************************************************************/ #endif /*DISABLE_DKIM*/ /* End of File */