--- res/res_pjsip_sdp_rtp.c	(Asterisk 13.21.1)
+++ res/res_pjsip_sdp_rtp.c	(working copy)
@@ -1133,5 +1133,5 @@
 			if (hash == AST_RTP_DTLS_HASH_SHA1) {
-				ast_str_set(&fingerprint, 0, "SHA-1 %s", crypto_attribute);
+				ast_str_set(&fingerprint, 0, "sha-1 %s", crypto_attribute);
 			} else {
-				ast_str_set(&fingerprint, 0, "SHA-256 %s", crypto_attribute);
+				ast_str_set(&fingerprint, 0, "sha-256 %s", crypto_attribute);
 			}
--- channels/chan_sip.c	(Asterisk 13.21.1)
+++ channels/chan_sip.c	(working copy)
@@ -13094,3 +13094,3 @@
 	if (fingerprint && (hash == AST_RTP_DTLS_HASH_SHA1 || hash == AST_RTP_DTLS_HASH_SHA256)) {
-		ast_str_append(a_buf, 0, "a=fingerprint:%s %s\r\n", hash == AST_RTP_DTLS_HASH_SHA1 ? "SHA-1" : "SHA-256",
+		ast_str_append(a_buf, 0, "a=fingerprint:%s %s\r\n", hash == AST_RTP_DTLS_HASH_SHA1 ? "sha-1" : "sha-256",
 			fingerprint);