DBMS_CRYPTO.mac(UTL_I18N.string_to_raw(l_oauth_base_string, 'AL32UTF8') 
               ,DBMS_CRYPTO.hmac_sh1 
               ,UTL_I18N.string_to_raw(l_oauth_key, 'AL32UTF8'));

 publicstatic String calculateRFC2104HMAC(String data, String key)
 throwsSignatureException, NoSuchAlgorithmException, InvalidKeyException
 {
   SecretKeySpecsigningKey = new SecretKeySpec(key.getBytes()
                                             , HMAC_SHA1_ALGORITHM);
   Macmac = Mac.getInstance(HMAC_SHA1_ALGORITHM);
   mac.init(signingKey);
   returntoHexString(mac.doFinal(data.getBytes()));
 }

CREATE OR REPLACE package jmj_hash_util_pkg AS
  FUNCTION sha1(p_buffer in raw) RETURN sha1_checksum_raw;
END jmj_hash_util_pkg;

FUNCTION hmac_sha1(p_message IN VARCHAR2, p_key IN VARCHAR2)
  RETURN VARCHAR2 IS

     -- Binaries
     v_ohsh   RAW(32767);
     v_kpad   RAW(32767);
     v_ipad   RAW(32767);
     v_opad   RAW(32767);
     v_ihsh   RAW(32767);
     v_skey   RAW(32767);
     v_key_in VARCHAR2(1000);
     v_key    RAW(32767);

     -- Result as hex in the form of text
     v_return VARCHAR2(2000);

  BEGIN

    v_key_in := p_key;

    -- Keys longer than 64 bytes must first be hashed
    IF utl_raw.length(sys.utl_raw.cast_to_raw(v_key_in)) > 64 THEN
      v_key := jmj_hash_util_pkg.sha1(sys.utl_raw.cast_to_raw(v_key_in));
    ELSE
      v_key := sys.utl_raw.cast_to_raw(v_key_in);
    END IF;

    -- Pad the key with zeroes to 64 bytes (128 characters)
    v_kpad := jmj_util_pkg.pad_key(64,'00');

    -- XOR with 64 characters of 0x36 HEX
    v_ipad := jmj_util_pkg.xor(v_ipad,'36');

    -- XOR with 64 characters of 0x5c HEX
    v_opad := jmj_util_pkg.xor(v_kpad,'5c');

    -- Inner HMAC1 hash with inner key and message
    SELECT jmj_hash_util_pkg.sha1(v_ipad || nvl(sys.utl_raw.cast_to_raw(p_message),'') )
    INTO   v_ihsh FROM dual;  

    -- Outer HMAC1 hash with inner hash
    SELECT jmj_hash_util_pkg.sha1(v_opad || v_ihsh )
    INTO   v_ohsh FROM dual;

    -- Convert back to HEX for return value
    SELECT lower(rawtohex(v_ohsh))
    INTO   v_return FROM dual;

    RETURN v_return;

  END;

SELECT jmj_hmac_pkg.hmac_sha1('','') actual 
,      'fbdb1d1b18aa6c08324b7d64b71fb76370690e1d' answer
FROM   dual
UNION ALL
SELECT jmj_hmac_pkg.hmac_sha1('The quick brown fox jumps over the lazy dog','key') actual
,      'de7c9b85b8b78aa6bc8a7a36f70a90701c9db4d9' answer
FROM   dual
UNION ALL
SELECT jmj_hmac_pkg.hmac_sha1('ABC','iDho0Xmt0PT4J3Ke1BCMbg4voR58CvOJ5miMShLbYAgFegwtk2kJiJM2TOiJR1CzWyL3QUC1VTBdS6IU')
  ,   'f5191e56e2aa2c73f8be0c717478c47b6dcae8c5' -- LONG KEY TEST
FROM dual

ACTUAL                                   ANSWER                                  
---------------------------------------- ----------------------------------------
fbdb1d1b18aa6c08324b7d64b71fb76370690e1d fbdb1d1b18aa6c08324b7d64b71fb76370690e1d
de7c9b85b8b78aa6bc8a7a36f70a90701c9db4d9 de7c9b85b8b78aa6bc8a7a36f70a90701c9db4d9
f5191e56e2aa2c73f8be0c717478c47b6dcae8c5 f5191e56e2aa2c73f8be0c717478c47b6dcae8c5