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feat: plaintext length pre-validation in rsa_crypt() #135

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Merged
atoomic merged 2 commits into from
Apr 3, 2026
Merged

feat: plaintext length pre-validation in rsa_crypt() #135

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41667cc
feat: add plaintext length pre-validation in rsa_crypt()
Koan-Bot Mar 21, 2026
658b51e
rebase: apply review feedback on #135
Koan-Bot Mar 21, 2026
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34 changes: 29 additions & 5 deletions RSA.xs
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Original file line number Diff line number Diff line change
Expand Up @@ -343,7 +343,7 @@ SV* rsa_crypt(rsaData* p_rsa, SV* p_from,
#else

SV* rsa_crypt(rsaData* p_rsa, SV* p_from,
int (*p_crypt)(int, const unsigned char*, unsigned char*, RSA*, int), int is_encrypt)
int (*p_crypt)(int, const unsigned char*, unsigned char*, RSA*, int), int public, int is_encrypt)
#endif
{
STRLEN from_length;
Expand All @@ -361,6 +361,30 @@ SV* rsa_crypt(rsaData* p_rsa, SV* p_from,
"Use use_pkcs1_oaep_padding() for encryption, or use_pkcs1_padding() with sign()/verify().");
}

/* Pre-validate plaintext length before calling OpenSSL.
Only applies to encryption direction (encrypt, private_encrypt),
not to decryption (decrypt, public_decrypt) where input is ciphertext. */
if (public == is_encrypt) {
int max_len = -1;
const char *pad_name = NULL;

if (p_rsa->padding == RSA_PKCS1_OAEP_PADDING) {
max_len = size - 42; /* 2 * SHA1_DIGEST_LENGTH + 2 */
pad_name = "OAEP";
} else if (p_rsa->padding == RSA_PKCS1_PADDING) {
max_len = size - 11; /* PKCS#1 v1.5 overhead */
pad_name = "PKCS#1 v1.5";
} else if (p_rsa->padding == RSA_NO_PADDING) {
max_len = size;
pad_name = "no";
}

if (max_len >= 0 && (int)from_length > max_len) {
croak("plaintext too long for key size with %s padding"
" (%d bytes max, got %d)", pad_name, max_len, (int)from_length);
}
}

#if OPENSSL_VERSION_NUMBER >= 0x30000000L

if(p_rsa->padding == RSA_PKCS1_PSS_PADDING) {
Expand Down Expand Up @@ -898,7 +922,7 @@ encrypt(p_rsa, p_plaintext)
#if OPENSSL_VERSION_NUMBER >= 0x30000000L
RETVAL = rsa_crypt(p_rsa, p_plaintext, EVP_PKEY_encrypt, EVP_PKEY_encrypt_init, 1 /* public */, 1 /* is_encrypt */);
#else
RETVAL = rsa_crypt(p_rsa, p_plaintext, RSA_public_encrypt, 1 /* is_encrypt */);
RETVAL = rsa_crypt(p_rsa, p_plaintext, RSA_public_encrypt, 1 /* public */, 1 /* is_encrypt */);
#endif
OUTPUT:
RETVAL
Expand All @@ -915,7 +939,7 @@ decrypt(p_rsa, p_ciphertext)
#if OPENSSL_VERSION_NUMBER >= 0x30000000L
RETVAL = rsa_crypt(p_rsa, p_ciphertext, EVP_PKEY_decrypt, EVP_PKEY_decrypt_init, 0 /* private */, 1 /* is_encrypt */);
#else
RETVAL = rsa_crypt(p_rsa, p_ciphertext, RSA_private_decrypt, 1 /* is_encrypt */);
RETVAL = rsa_crypt(p_rsa, p_ciphertext, RSA_private_decrypt, 0 /* private */, 1 /* is_encrypt */);
#endif
OUTPUT:
RETVAL
Expand All @@ -932,7 +956,7 @@ private_encrypt(p_rsa, p_plaintext)
#if OPENSSL_VERSION_NUMBER >= 0x30000000L
RETVAL = rsa_crypt(p_rsa, p_plaintext, EVP_PKEY_sign, EVP_PKEY_sign_init, 0 /* private */, 0 /* is_encrypt */);
#else
RETVAL = rsa_crypt(p_rsa, p_plaintext, RSA_private_encrypt, 0 /* is_encrypt */);
RETVAL = rsa_crypt(p_rsa, p_plaintext, RSA_private_encrypt, 0 /* private */, 0 /* is_encrypt */);
#endif
OUTPUT:
RETVAL
Expand All @@ -945,7 +969,7 @@ public_decrypt(p_rsa, p_ciphertext)
#if OPENSSL_VERSION_NUMBER >= 0x30000000L
RETVAL = rsa_crypt(p_rsa, p_ciphertext, EVP_PKEY_verify_recover, EVP_PKEY_verify_recover_init, 1 /*public */, 0 /* is_encrypt */);
#else
RETVAL = rsa_crypt(p_rsa, p_ciphertext, RSA_public_decrypt, 0 /* is_encrypt */);
RETVAL = rsa_crypt(p_rsa, p_ciphertext, RSA_public_decrypt, 1 /* public */, 0 /* is_encrypt */);
#endif
OUTPUT:
RETVAL
Expand Down
49 changes: 48 additions & 1 deletion t/crypto.t
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Expand Up @@ -7,7 +7,7 @@ use Crypt::OpenSSL::RSA;
# Tests for encrypt/decrypt error paths, boundary conditions, and edge cases.
# These cover gaps not addressed by rsa.t or padding.t.

plan tests => 12;
plan tests => 20;

Crypt::OpenSSL::Random::random_seed("OpenSSL needs at least 32 bytes.");
Crypt::OpenSSL::RSA->import_random_seed();
Expand Down Expand Up @@ -119,3 +119,50 @@ $rsa->use_pkcs1_oaep_padding();
eval { $rsa->encrypt("test") };
ok($@, "PSS padding cannot be used for encryption");
}

# --- Plaintext length pre-validation error messages ---

# OAEP: clear message with byte counts
{
$rsa->use_pkcs1_oaep_padding();
my $too_long = "x" x ($oaep_max + 1);
eval { $rsa->encrypt($too_long) };
like($@, qr/plaintext too long for key size with OAEP padding/,
"OAEP oversized plaintext gives clear error message");
like($@, qr/\Q$oaep_max bytes max\E/,
"OAEP error includes max byte count");
my $got = $oaep_max + 1;
like($@, qr/got $got/,
"OAEP error includes actual byte count");
}

# PKCS#1 v1.5 via private_encrypt: clear message
{
$rsa->use_pkcs1_padding();
my $pkcs1_max = $key_size - 11;
my $too_long = "x" x ($pkcs1_max + 1);
eval { $rsa->private_encrypt($too_long) };
like($@, qr/plaintext too long for key size with PKCS#1 v1\.5 padding/,
"PKCS#1 v1.5 oversized plaintext gives clear error message");
like($@, qr/\Q$pkcs1_max bytes max\E/,
"PKCS#1 v1.5 error includes max byte count");
}

# no-padding: clear message
{
$rsa->use_no_padding();
eval { $rsa->encrypt("x" x ($key_size + 1)) };
like($@, qr/plaintext too long for key size with no padding/,
"no-padding oversized plaintext gives clear error message");
}

# Decrypt still works (no false positive from validation)
{
$rsa->use_pkcs1_oaep_padding();
my $ct = $rsa->encrypt("validation bypass test");
my $pt = eval { $rsa->decrypt($ct) };
ok(!$@, "decrypt not affected by plaintext length validation")
or diag $@;
is($pt, "validation bypass test",
"decrypt returns correct plaintext after validation change");
}
2 changes: 1 addition & 1 deletion t/error_queue.t
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Expand Up @@ -28,5 +28,5 @@ like($second_error, qr/OpenSSL error: \S/, "second error has a meaningful OpenSS
# Trigger yet another failure after two eval-caught ones — error queue should be clean
eval { $rsa->encrypt("A" x 500) };
my $third_error = $@;
like($third_error, qr/too large|data greater|asym cipher failure/i,
like($third_error, qr/too large|data greater|asym cipher failure|plaintext too long/i,
"third error reports actual problem (data too large), not stale from earlier failures");
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